Computer Science XI

Computer System Unit 1 … 33.
Figure: 1.14 Block diagram of a typical digital computer

MEMORY

CONTROL OUTPUT UNIT
REGISTERS
INPUT UNIT

ALU

CPU

Indicates control signals
Indicates flow of information

The components of a computer can be categorized into two types- processing hardware, called processor,
that processes the data according to the instructions, and peripherals that are used to input, output and
communicate, or to store the data and results. The different components of a typical digital computer and
their major functions are described below.

Input Unit

The input unit is a device that is used to feed the data and instructions into the computer. The input can be
entered either by typing on the keyboard or by using point and click devices. Input devices present data to
the processing unit in machine readable form. Keyboard and mouse are commonly used as input devices.
There are many other input devices; like OCR, scanner, graphic tablet, light pen etc which can be used as
input devices. All the input devices perform the following functions.
● Accept the data and instructions from the outside world.
● Convert it to a form that the computer can understand.
● Supply the converted data to the computer system for further processing.

Central Processing Unit (CPU)

CPU is a major component of any computer system. It acts as heart and brain of computer, and performs
all the processing related activities. Therefore, the processing unit is popularly known as Central
Processing Unit (CPU). It receives data and instructions from outside world, stores them temporarily,
processes the data as per the instructions and sends the result to the outside world as information. The
CPU performs the following functions:
● It performs all calculations.
● It takes all decisions.
● It controls all units of the computer.

It is the component of a computer system with the circuitry to control the interpretation and
execution of instructions. It performs the process part of INPUT-PROCESS-OUTPUT cycle.
The CPU is a combination of three components ALU, CU and Register Array. These three
components are described below;

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Arithmetic Logic Unit (ALU)

It contains electronic circuits necessary to perform all the arithmetic and logical operations. All
calculations are performed in the Arithmetic Logic Unit (ALU) of the computer. It also does comparison
and takes decision. The arithmetic operations include addition, subtraction, multiplication, division, etc.
Similarly this unit also executes the logic operations. The logical operations include Comparison, Shift,
Rotate, AND, OR, Complement. ALU answers the questions like YES/NO, TRUE/FALSE,
GREATER/SMALLER, WRITE/WRONG etc. Whenever calculations are required, the control unit
transfers the data from storage unit to ALU once the computations are done, the results are transferred to
the storage unit by the control unit and then it is send to the output unit for displaying results.

Control Unit (CU)

It controls all other units in the computer. The control unit instructs the input unit, where to store the data
after receiving it from the user. It controls the flow of data and instructions from the storage unit to ALU.
It also controls the flow of results from the ALU to the storage unit. The control unit is generally referred
as the central nervous system of the computer that control and synchronizes its working.

The task of the control unit is to carry out the fetch-execute cycle over and over and over again:
1. Fetch the next instruction from memory.
2. Decode the instruction.
3. Execute the instruction.

Register Array

It is a memory of a processor. It is used by processor only for at the time of execution and storing
temporarily. CPU contains a number of registers like Accumulator, Stack Pointer, and Address Register
etc. It is a special temporary storage location within the CPU. Registers quickly accept, store and transfer
data, instructions, and result that are being used immediately. To execute an instruction, the control unit of
the CPU retrieves it from main memory and places it onto a register. Registers
● can be thought of as fast memory locations;
● are relatively few in number (e.g., 16 or 32);
● are typically large enough to hold a single integer or floating point number;
● are used to hold inputs to, and outputs from, the arithmetic and logical operations;
● are used for temporary storage of intermediate results.

Memory

Memory is the location where data and programs entered through the input unit are stored. It preserves
the intermediate and final results before these are sent to the output devices. It also saves the data for the
future reference. Memory is the main storage unit in a computer. In simple terms, memory indicates the
primary memory. But, memory can be divided into two types- primary or main memory and secondary or
auxiliary memory.
The primary memory is a temporary but the main memory of the computer. It stores and provides the
information very quickly. This memory is generally used to hold the program being currently executed in
the computer, the data being received from the input unit, and the intermediate and final results of the
program. RAM is an example of main memory. Data stored in main memory is volatile and is erased as
soon as the power supply is cut off. In order to store the data permanently, the data has to be transferred
to the permanent memory. Therefore, secondary memory, which is a permanent memory, is used to store
data.

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Computer System Unit 1 … 35.

The secondary memory has very large storage capacity, and is used as an archive or back up memory for
future reference. It stores several programs, documents, data bases etc. The programs that you run on the
computer are first transferred to the primary memory before it is actually run. Whenever the results are
saved, again they get stored in the secondary memory. Hard disk, floppy disk, compact disk etc are
examples of secondary memory.
The cost of the primary storage is more compared to the secondary storage. Therefore most computers
have limited primary storage capacity. The secondary memory is slower and cheaper than the primary
memory.

Output Unit

An output unit of a computer is a peripheral device that provides the information and results of a
computation to outside world. It communicates information to humans or another machine by accepting
data from the computer and transforming them into a usable form. The output device gives the desired
result to the user.
Printers, Plotters, Visual Display Unit (VDU) like CRT and LCD monitor, Multimedia projector, are the
commonly used output devices. Other commonly used peripheral devices are floppy disk drive, hard disk
drive, and magnetic tape drive.
Therefore, an output device is a peripheral device that allows a computer to communicate information to
humans or another machine by accepting data from the computer and transforming them into a usable
form. The output devices give the desired result to the user.

MICROPROCESSOR

It is a processing unit called Microprocessor. The Microprocessor is an entire CPU built in a single chip.
We know that the central processing unit (CPU) contains three separate components- the ALU, CU and the
Register array. When all these three components are fabricated on a single chip to form a complete
computation system engine, then the CPU is commonly known as the microprocessor. In a
microcomputer, a silicon chip that contains the components of the CPU is mounted on the main circuit
board, called the “motherboard”. A microprocessor chip contains the circuits and special storage locations
called “registers” needed to perform the arithmetic-logic and control functions. The registers used in a
microprocessor are identified as B, C, D, E, H and L. Microprocessor is an integrated circuit with VLSI or
higher level of integration. The third generation computers used integrated circuits with SSI & MSI, while
the fourth generation computers started using VLSI semiconductor chip called microprocessor as central
processing unit. The computer that uses microprocessor as its CPU is known as a microcomputer. In the
world of personal computers, the terms microprocessor and CPU are used interchangeably.

Figure: 1.15 Components of microprocessor Figure: 1.16 Microprocessor chip

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Microprocessors can be differentiated based on the following three basic characteristics;

● Instruction set: Depending on the type of microprocessor or brand or version of computer, the set of
instructions that the microprocessor can execute can vary.

● Bandwidth : The number of bits processed in a single instruction can also vary, such as 8-bits
processor, 16 bit processor or 32 bits processor or 64 bits processor etc.

● Clock speed : The clock speed determines how many instructions per second the processor can
execute. It is measured in Mega Hertz or Giga Hertz. The higher the value, the more powerful the
CPU. For example, a 32-bit microprocessor that runs at 50MHz is more powerful than a 16-bit
microprocessor that runs at 25MHz.

The microprocessor is the heart of any normal computer, whether it is a desktop machine, a server or
a laptop. Microprocessors also control the logic of almost all
digital devices, from clock radios to fuel-injection systems for
automobiles. The first microprocessor was the Intel 4004,
introduced in 1971. The 4004 was not very powerful -- all it
could do was add and subtract, and it could only process 4 bits
at a time. It was manufactured as a SSI & MSI chip having 2,300
transistors, 640 bytes of memory addressing capacity, and a 108
KHz clock. But, everything was on one chip. Prior to the 4004,
engineers built computers either from collections of chips or
from discrete components (transistors wired one at a time). The
4004 powered one of the first portable electronic calculators. Microprocessor technology has also gone
many advancements along with the change in integration technology, speed, address and data bus
capacity, addressable memory etc. The Intel Pentium 4 which was introduced in 2000 AD used VLSI
technology with 42 million transistors. It has 1.4 GHz clock speed, 36-bit address bus, 64-bit data bus
and 64 Gigabyte addressable memory. Likewise 10th Generation Intel® Core TM i9- 10900K Processor
introduced 2020 AD having 64 bit processor with 5.30 GHz clock speed and 10 Core with 20 threads
having 20 MB Intel® Smart cache.

The different components of microprocessor and their functions have already been discussed in the
previous section. (Therefore, refer to the previous section for the description of components of

Microprocessor and their functions).

Microprocessor being the central component of a computer performs the following functions;

1. Receives instructions and data from input units

2. Reads instructions and data from memory

3. Decodes the instructions and generates control signals for different components to control their
operations.

4. Processes data or makes decisions based on the instructions

5. Provides result to the outside world as information

In addition, a microprocessor can be used in;

● Turning traffic lights (street light) ON and OFF.

● Computing mathematical functions

● Making decisions

● Keeping track of guidance system (e.g. missile tracking or pilotless plane tracking)

● Automating and controlling the industrial processes and operations

● Operating or controlling microprocessor based products and systems, and many more.

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Computer System Unit 1 … 37.

CONCEPTS OF SYSTEM BUSES

A bus is a data communication path over which bits of information are transmitted between the various
computer components. The CPU has to be able to send various data, instructions, and information to all
the devices and components inside the computer as well as to the different peripherals. These electronic
pathways are nothing more than tiny wires that carry information, data and different signals throughout
the computer from one component to the other components. This network of wires or electronic pathway
is commonly known as the 'System Bus' or simply ‘Bus’.

According to the connection of components inside and outside the board, basically bus can be divided into
two different types, Internal (System) bus and External (Expansion) bus. The Internal bus connects the
different components inside the system- the CPU, system memory, and all other components on the
motherboard. It's also referred to as the System Bus.

The External Bus connects the different external devices, peripherals, expansion slots, I/O ports and drive
connections to the rest of the computer. In other words, the External Bus allows various devices to be
added to the computer. It allows for the expansion of the computer's capabilities. It is generally slower
than the system bus. Another name for the External Bus is the Expansion Bus or slot. The expansion slot
can be:

1. ISA bus: It stands for Industry Standard Architecture. It has been used in the past for plug-in
modems, sound cards, and various other low-speed peripherals. It was used before the use of PCI
slot.

2. AGP bus: It stands for Accelerated Graphics Port. This is a 32-bit bus designed specifically for a

video card.

3. PCI bus: It stands for Peripheral Component Interconnect. It connects the CPU and expansion boards
such as modem cards, network cards and sound cards.

4. USB: This is an external bus standard that supports data transfer rates of 12 Mbps. A single USB port
connects up to 127 peripheral devices, such as mice, modems, and keyboards.

5. SCSI: Short for Small Computer System Interface, a parallel interface standard used by Apple
Macintosh computers, PCs and Unix systems for attaching peripheral devices to a computer. Etc.

Depending on the type of information carried, bus can be divided into three types (as shown in fig below).
They are:

● Control (also called timing and control) bus

● Address bus, and

● Data (also called a memory bus) bus.

Figure: 1.17 Processor

Processor Control Bus
Address Bus

Data Bus

Input Memory Output

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1. Control Bus: The control bus is used by the CPU to direct and monitor the actions of the other
functional areas of the computer. It is used to transmit a variety of individual signals (read, write,
interrupt, acknowledge, and so forth) necessary to control and coordinate the operations of the
computer. The control bus is unidirectional- from CPU to other components.

2. Address Bus: The address bus consists of all the signals necessary to define any of the possible
memory address locations within the computer, or for modular memories any of the possible
memory addresses locations within a module. An address is defined as a label, symbol, or other set
of characters used to designate a location or register where information is stored. Before data or
instructions can be written into or read from memory by the CPU, an address must be transmitted to
memory over the address bus. This means, Address bus connects only the CPU and memory and
carries only memory addresses. The address bus is also unidirectional-from CPU to memory.

3. Data Bus: The bidirectional data bus, sometimes called the memory bus, handles the transfer of all
data and instructions between functional areas of the computer. The bidirectional data bus can only
transmit in one direction at a time. The data bus is used to transfer instructions from memory to the
CPU for execution. It carries data (operands) to and from the CPU and memory as required by
instruction translation. The data bus is also used to transfer data between memory and the I/O
section during input/output operations. According to how much it transfers data, the bus can be
called 1 bit, 8 bits, 16 bits, 32 bits, or 64 bits data bus.
Like the processor, the bus speed is measured in megahertz (MHz) because it has its own clock
speed. As we know, the faster the bus clock speed, the faster it can transfer data between parts of the
computer. The majority of today’s PCs have a bus speed of either 100 MHz or 133 MHz, but higher
speeds are becoming more common.

MEMORY

Memory is a location or space where we can keep data, information, and programs temporarily as well as
permanently. It is one of the major components of computer system. Without memory, system cannot run
and store the data. Memory is necessary to store, process, and load (display) the data. It can be internal or
external. Moreover, the term memory is usually used as shorthand for physical memory, which refers to
the actual chips capable of holding data. Some computers also use virtual memory, which expands
physical memory onto a hard disk.
Memory can be basically classified into two major categories. They are;
1. Primary Memory or Main memory, Internal memory and
2. Secondary memory or Auxiliary memory or External memory
CPU registers, cache memory, RAM, ROM, Hard disk, Floppy disk or Magnetic tape etc are all memory
devices used for loading or storing data and instructions. The different types of memories are shown in the
figure below as memory hierarchy. The memory hierarchy depicts the relationship of memory devices
with the CPU depending on the increase in cost, and speed, and decrease in capacity, and size while
moving towards CPU.

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Computer System Unit 1 … 39.
Figure: 1.18 Memory hierarchy in a computer system

High Cost Registers Size
Fast Speed
Cache

Primary Memory
(RAM, ROM)

Secondary Memory
(Hardisk, Flopy, Magnetic

tape, CD, DVD etc)

Primary Memory

Primary Memory is a semiconductor chip memory. Generally, this type of memory is used for temporary
storage and data processing. This memory consists of hundreds of thousands of cells called "storage
locations" each capable of storing one word of information. This memory is called by different names, like
internal storage, primary storage, main memory or simply memory. Without this memory, computer
system cannot even open and run. Primary memory can be volatile or non-volatile. RAM is a volatile
memory and ROM is a non-volatile memory. This memory is not for backup storage. It is typically
extremely fast in modern computers, and since it interfaces almost directly with the CPU, it allows for very
fast transfers between the two. It is costly, fast, and small in size as compared to secondary memory.
Primary memory is of two types: one is RAM and another one is ROM.

RAM

RAM stands for Random Access Memory. RAM is
considered “random access” because any word in the
memory can be directly accessed in any order. RAM
also refers to read and write memory; that is, we can
both write data randomly into and read data from
RAM. This is in contrast to ROM, which permits you
only to read data. Actually, the primary or main
memory is referred to as RAM. It is volatile in nature. It
means, data is stored on it until the power is switched
on. Without RAM, computer cannot open and run. Every time, when the power is switched on, the system
files are load into this memory from the storage device such as a hard disk. Therefore, it is also called the
loading memory.

The RAM plays very important role in data processing. The program and the data must be transferred to
RAM before running the program to process the data. The processor processes the data according to the
program instructions by fetching the data and instructions from the RAM. The processor interprets and
executes the program instructions while the program is in RAM.

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The storage capacity of RAM or main memory is measured in bytes. A byte is a group of 8-bits. One
character takes one byte of memory. The amount of data and program size are also measured in bytes.

1 Byte = 8-Bits

1 Kilo Byte = 1024 Bytes

1 Mega Byte = 1024 Kilo Bytes

1 Giga Byte = 1024 Mega Bytes

1 Tera Byte = 1024 Giga Bytes

More RAM means the computer can use powerful program with large size. It also improves the data
accessing and processing speed of the computer. RAM plays an important role in the internal operation of
the processor. Microcomputers come with different capacity of RAMs which can be from MB to few GBs.
RAM can be further divided into DRAM and SRAM.

i. DRAM
DRAM stands for Dynamic Random Access Memory. DRAM is the most common type of RAM used
to access data & instructions in micro computers. DRAM has memory cells with a pair of transistor
and capacitor requiring constant refreshing. DRAM has high packing density as each cell occupies
very small space on a chip, and is therefore cheaper. During the refreshing process the CPU has to
wait to read & write data in DRAM. It is because DRAM decreases the processing speed of the
computer. Refreshing is a process of recharging the capacitor. An extra circuitry and power supply
such as battery is required for refreshing the DRAM.
DRAM can also be divided into SDRAM and RDRAM. SDRAM stands for Synchronous Dynamic
RAM. SDRAM are much faster than basic DRAM chips because they are synchronized to the system
clock. Often in computer ads, the speed of SDRAM is expressed in megahertz (MHz). RDRAM stands
for Rambus Dynamic RAM. It is faster and more expensive than SDRAM because it uses pipelining
technique. It is used in Intel P4 and above. Today most of PCs use SDRAM or RDRAM.

ii. SRAM
SRAM stands for Static Random Access Memory. It uses multiple transistors, typically four to six, for
each memory cell but doesn’t have a capacitor in SRAM cells, and does not need refreshing circuits.
Each cell takes more space on a chip and therefore SRAM has less packing density and is costly. It is
faster than DRAM, but more expensive than DRAM chips. Special applications such as cache and
ROM use SRAM chips.

ROM

ROM stands for Read Only Memory. The ROM contains instructions that are permanently stored on the
chips by the manufacturers themselves. In fact recording data and
instructions permanently into this kind of memory is called "burning
in the data". The instructions stored in ROM can only be read but
cannot be modified. This is the reason why it is called Read Only
Memory. Data stored in these chips is either unchangeable or requires
a special operation or device called burner to change the information
stored in ROM chips.
ROM is a semiconductor static chip programmed at the time of its manufacture and is not re-
programmable by the user. The programs stored in ROM are called firmware. Firmware is a combination
of hardware and software in a single device like ROM. ROM is a non-volatile memory. The contents of
ROM are not lost even after switching off the computer.

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Computer System Unit 1 … 41.

The ROM contains the Basic Input / Output System (BIOS) which is a set of instructions that are
automatically activated when the computer is turned on. It means that computer uses the instructions on
ROM at the time of booting for the following purposes.

● To check different components of computer system.

● To load the operating system into computer memory etc.

Many other devices also contain ROM chips. For example a printer has a ROM chip that contains data or
information for fonts. The ROM is further divided into Masked ROM and Field Programmable ROM.
Masked ROM is simply a ROM, and Field programmable ROM is a ROM which can be programmed by
the user. It can be divided into PROM, EPROM, and EEPROM.

1. PROM

2. EPROM

3. EEPROM

1. PROM
PROM stands for Programmable Read Only Memory. PROM is a blank ROM chip on which the user
can write his own program instructions and data, but only once. However once the program or data
is written into PROM chip, it cannot be changed. The programmer uses micro-code instructions to
write information in a PROM chip. Once the programmer writes the micro-code on the PROM chip, it
functions like a normal ROM chip.

2. EPROM

Once the ROM or PROM is programmed, its contents cannot be changed. However there is another
type of memory chip called EPROM that overcomes this problem. EPROM stands for Erasable
Programmable Read Only Memory. Like PROM, it is initially blank and the user or manufacture can
write his own program or data by using special devices. Unlike PROM, the data written in EPROM
chip can be erased and reprogrammed by exposing the chip into high intensity ultraviolet light for 10
to 20 minutes. This memory chips are used to store programs that need updating. So program or data
written in EPROM chip can be changed and new data can also be added on this type of ROM. When
EPROM is in use, its contents can only be read.

3. EEPROM

EEPROM means Electrically Erasable Programmable Read Only Memory. An EEPROM is a special
type of PROM that can be erased by exposing it to a relatively high (21 Volts) voltage of an electrical
charge on byte by byte basis without the necessity of chip being removed from the computer. The
erasing requires much short time in millisecond range and EEPROM can be reprogrammed up to
10000 times.

Cache Memory

The cache is also a kind of primary memory. It is meant to improve access times and enhance the overall
performance of the computer. Cache is the way that most CPUs are matched to RAM. In between the CPU
and system memory, there is a small cache memory of the faster SRAM. It is a nifty feature of most CPUs
which makes use of the fact that some parts of RAM are accessed more often than others by storing certain
amounts of data in a cache. Instead of retrieving the data from RAM, the CPU retrieves it from the cache,
which is much faster to access since it is located on the CPU itself or near the CPU. If the data is in the
cache, it's called a 'cache hit' and is retrieved at a faster speed than it would be from system memory. If it
isn't in the cache, then it's called a 'cache miss' and the information is retrieved from system memory. The
number of cache hits, far out number the misses and this speeds up system performance dramatically.

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Two factors that affect the cache's performance are - level and size. The level indicates connecting circuits
or electronic pathways and physical proximity to the CPU and the size indicates the capacity. There are
two types of caches internal (L1) and External (L2) based on the level.

Internal Cache (Level I or L1)
Internal cache is a small amount of SRAM that is placed inside the CPU that is accessed directly. It runs at
the same speed as the processor, and enhances the performance. It is also called Level I or L1 cache.

External Cache (Level II or L2)
External Cache is separate or external from the CPU. It's often socketed on the motherboard. Level 2
caches, is effectively a cache for the cache, further enhancing the computer's overall speed. Irrespective of
the speed of CPU, the external cache is limited to the speed of the system bus. External cache is often
called Level II, or L2 cache. L2 cache is generally much larger than L1 cache, such as L1 generally has 16K-
64K capacity, and L2 has 512K or 1MB etc.

Buffer

Buffer is used for an uninterrupted flow of information, especially, when there is faster device transferring
the data to a slower device. Due to the mismatch between the processing speeds of two devices, a faster
device may drown the slower device with an overload of data. Therefore, the data transferred by a faster
device is first saved into a memory called the buffer until the slower device completes its current task and
reads next data from the buffer in sequence one after another. Therefore, buffer is an intermediate
temporary storage location in memory between two Buffer devices. Buffer is generally created in primary
memory (RAM) rather than in other memories because reading data from RAM is faster than from other
devices. Some hardware devices use their own buffer memory rather than RAM, such as in printers. The
CPU transfers the data to the printer, and the printer stores the new data into its own buffer until it
finishes its current print operation. Once the printer completes the current job, the next job is read from the
print buffer, and continues its operation. The buffer is also used in streaming online multimedia content
while playing the music and video from the Internet.

Secondary Memory

The main memory of the computer is volatile. It cannot be used as permanent storage because when
computer is switched off, its contents are erased. Its storage capacity is also very small. Therefore, to
overcome these limitations of primary memory, a memory is required which is permanent and has large
capacity. This later category of memory is called secondary memory. While primary memory is concerned
mainly with storing programs currently executing and, data currently being accessed, secondary memory
is generally intended for storing anything that needs to be kept even if the computer is switched off or no
programs are currently executing.

Secondary memory is also known as auxiliary or backup memory or simply the storage. A secondary
storage media is the physical material on which data and programs are stored on a long term basis or for
future reference. It is non-volatile, meaning that it retains its contents even when power to the computer
system is switched off. A large amount of data and programs can be stored on it. Its storage capacity is up
to Gigabytes (GB) for personal computers. Data and programs on the secondary memory are organized
into files-named sections of storage. The application software and system software are stored on the
secondary storage.

Removability for some forms of secondary memory is an additional bonus, allowing data to be shared
between multiple computers on disks. An important aspect of secondary memory is that it cannot be
addressed directly by the CPU. Examples of secondary storage are floppy disk, Zip disk, hard disk,
magnetic tape, CDs and DVDs.

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The speed of storage device and memory is defined by access time. The access time of storage device is
measured as the amount of time that a storage device takes to locate and retrieve a specific data on the
storage medium. Similarly, the access time of RAM is measured as the time required delivering data from
RAM to the processor. The access time of storage device is slower than access time of primary memory.

Types of Secondary Memory

As discussed earlier, secondary storage is a long term non volatile or permanent memory. This means it
stores and retains the programs and data even after the computer is switched off. It is used as a backup
memory for future reference. The storage devices can be categorized into various types: They are based on
Data Access, Storage Technology and External storage.

Based on the type of data access. They are sequential access and random access.

1. Sequential access: In sequential access devices, the data is written or read in sequence one after
another. We can't go directly to the desired location without going through all the preceding
locations. Magnetic tape like audio cassette is an example of sequential access media. They are slow
and used for backup purpose.

2. Random access: In contrast to sequential access, in random access storage devices, the data can be
written to any location or read from any location in random without going through the preceding
points. Random access storage is also called direct access because any data from or to any location
can be read or written directly. Magnetic disks, optical disks etc are some example of random
storage.

Random access is much faster than the sequential access, and the random access uses more than one
read write head while the sequential access uses only one head. Moreover, in the case of random
access, both the read/write head and the storage media can move forth and back and rotate as
required, while in the case of sequential access, the storage media alone can move and the read/write
head is stationary.

Based on the technology, the storage devices can be divided into semiconductor memory, magnetic
storage and optical storage.

1. Semiconductor Storage: The semiconductor memory is built of from the semiconductor devices like
transistors and gates. RAM, Cache and ROM are examples of semiconductor memory. They are very
fast and utilize completely random access method to read or write the data. Semiconductor memories
are generally used for primary storage. RAM, ROM, and Cache are already discuss above. Memory
card and Flash memory (Pen drive) also the semiconductor memory.

2. Magnetic Storage Memory: In magnetic storage, magnetic properties are used to read or write the
data. The magnetization of the magnetic material on the disk changes the orientation of magnetic
particles to store data.

"Magnetic storage" refers to systems that keep information or data on a magnetized material. In this
technology data is stored and read with the help of magnetic properties developed while applying
electricity on a magnetized medium. Magnetic storage uses different patterns of magnetization in a
magnetizable material to store data and is a form of non-volatile memory. The surfaces of diskette,
tape and disk are coated with magnetic material such as iron oxide or ferrous oxide, which can be
magnetized (i.e. which reacts to a magnetic field). The diskette drives, tape drives and disk drives are
used to write and read data to and from the diskettes, tapes and disks.

The surfaces of disks and magnetic tapes are coated with millions of tiny iron particles so that data
can be stored on them. Each of these particles can act as a magnet. The write/read heads of disk
drives or tape drives contain electromagnets that generate magnetic fields in the magnetic material
on the storage medium as the head passes over the disk or tape. The presence of a magnetic field
represents a ‘1’ bit and its absence represents a ‘0’ bit.

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The data reading process from magnetic disk or tape is a reverse process of writing. The storage
medium charges the magnet in the head, which causes a small current to flow through the head in
one direction or the other depending on the polarity of the field or the data. The disk or tape drive
senses the direction of the flow as the disk or tape passes by the head. In this way data is sent from
the read/write head into or from memory in the form of electric pulses. The information stored in a
disk can be read many times without affecting the stored data. So the reading operation is non-
destructive. But the writing of new data erases data previously stored at that location of the disk or
tape. The magnetic storage memory can be Floppy disk, Zip Disk, Hard disk, Magnetic tape, etc.
a. Magnetic (Hard) disk: Hard disk is a most commonly used storage device in personal
computers and laptops. Most application programs and operating systems require hard disk for
installation and operation. It contains one or more metal platters mounted on a central spindle,
like a stack of rigid diskettes. A hard disk is actually a stack of platters. Each platter is coated on
both sides with magnetic material. Both surfaces of each disk or platter are used to store
information except for the top and bottom platters. The hard disk and drive is a single unit. It
includes the hard disk, and the motor that rotates the platters. Each platter has two read/write
heads, one for each side. The hard disk has also arms that move the read/write heads to the
proper location on the platter to read or write data. The entire unit is enclosed in an airtight,
sealed case. The hard disk is, generally, not portable. It is permanently fixed with the system
unit. It is because hard disk is also referred to as fixed disk. (but, now a days, we can find
portable hard disks as well)
Figure: 1.19 Magnetic (Hard) Disk

A disk or platter has a flat circular shape. The surface of the disk is logically divided into
circular tracks, which are subdivided into sectors. The set of tracks of different platters that are
at a particular head position is referred to as cylinder.
However, the basic storage area (location) is sector. All sectors contained the same number of
bytes. Usually, in a single sector 512 bytes are stored. The total capacity of a disk can be
calculated by multiplying together, the following:
● Number of cylinders, which is the same as the number of tracks per surface.
● Number of read/write heads.
● Number of sectors per track.
● Number of bytes per sector.

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The storage capacity of hard disk in PCs is measured in Giga Bytes or Tera Bytes. 1TB hard
disks are common now a day. Like floppy disk, hard disk is formatted before using it as to store
data. Formatting is a process in which the operating system makes logical tracks on both sides
of each platter and divides each track into sectors. Each platter of hard disk has a very high
density. A large number of tracks are made on each surface of the platter. The performance of
the hard disk depends on the Seek Time, Rotational Latency, Transfer Time, and Access Time.
The rotation speed can be 5400, 7200, 10,000 or 16,000 rpm.

b. Floppy disk: A floppy disk is a magnetic storage media. The floppy disk is a thin and flexible
plastic disk made of up Mylar coated on both side with magnetic recording material (ferrous or
iron oxide). It is also called a diskette. It is packed in a stiff protected jacket made of plastic. IBM
invented the floppy disk in 1972. The size of the first floppy disk was 8-inch and had flexible
plastic cover. Next generation of floppies was 5.25 inches disk. Latest, the standard floppy disk
size is of 3.5 inch and has a rigid plastic cover. The size of disk refers to the diameter of disk.
The high-density disks are smaller in size but larger in storage capacity. The storage capacity of
floppy disk is very low (i.e. maximum storage capacity is 1.44 MB). It consists of number of
concentric tracks having number of sectors on each track. Each sector can store data up to 512
bytes. The average access time for the floppy disk is 150-250 ms. The rotation speed of disk is
360 rpm. It is slower than hard disk.

Figure: 1.20 Floppy disk

Typically, floppy disks are used to transfer small files to and from personal computers. Today,
floppy disks are not in much common use as they were ten years ago because of their low
storage capacity. The 3.5" diskette is also referred to as Micro Floppy Diskette. The read/write
window of micro disk is always closed with a Metal Shutter (sliding window). The shutter
automatically opens when the disk is inserted into the disk drive. The micro disk also has a
write-protected notch at one of its corners. A write protected-notch is a small opening that has a
tab can slide to cover the notch. If the write protected-notch is opened, the floppy drive cannot
write data on the disk. However, in this case data can be read only from the disk. To write data
on the disk, the write protected-notch must be closed.

c. Zip disk: A Zip disk is a type of portable magnetic media. Its storage capacity is about 100 MB
to 800 MB. It is used to back up important data. ZIP disk is similar to floppy disk but its storage
capacity is about 100 times greater than floppy disk. It is also more reliable storage medium
than floppy disk. Like floppy disk, the data can be easily transferred from one computer to
another by using Zip disk.

Figure: 1.21 Zip disk Figure: 1.22 disk drive

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A Zip disk drive is used to write and read data to and from the Zip disk. The Zip disk drive
cannot read data from floppy disk. Users use the external Zip drive, which can be connected to
the USB port or parallel port on the system unit to write and read data to and from the Zip disk.
Now a day, zip disk is not in much common use in personal computers.

d. Magnetic Tape: Magnetic tape is the most popular and oldest
storage medium used to store large amount of data and
instructions permanently. The magnetic tape is a plastic ribbon
with width 0.25 inch to 1 inch and one side coated with
magnetic recording material (ferrous-oxide or iron-oxide),
which can be magnetized. Data is stored on the tape in the form
of magnetic field, i.e. magnetized and non-magnetized spots
representing l’s and 0’s respectively. Like magnetic disk,
magnetic tape should also be formatted to store data on it. The
tape is divided into vertical columns called frames and each
frame is further divided into horizontal rows called tracks (or
channels). Each frame represents one character and each track of
frame stores one bit for the code of character.

Typically, a frame is divided into 9 tracks. The first 8 tracks are
used for recording the code of specific character and ninth track is used for recording the parity
bit or check bit. The parity bit is used to detect errors during reading or writing data on the
tape.

Like sound recording tape, the data and instructions on the magnetic tape can be recorded and
erased again and again. The amount of data that can be stored on a tape depends on its length,
its type and density. The storage capacity of tape is up to 100GB and offers an inexpensive way
to store a lot of data on a single cassette.

Magnetic tape a sequential storage media and is slower than the disks. Storing data on tapes is
considerably cheaper than storing data on disks. Unlike disks, tapes, generally, has single read
write head. Because tapes are slow, they are especially used for long term back up and
transportation. Data to be used frequently is almost always stored in disks.

3. Optical Storage Memory: But in the case of optical storage, the read write process uses optical
properties like laser beams. Today, somehow used and reliable storage devices are the optical storage
devices. These devices use laser technology i.e. laser light to write and read data to and from the
optical disk such as CDs (compact disks). The most popular optical storage devices are: CD-ROMs,
DVD-ROMs, CD-Recordable, and CD- Rewritable etc. Today, some PCs contain one CD or DVD
drive. A large amount of data, software, movies and songs can be stored on a single CD or DVD.
Some optical storage media is read-only while others are read and write.

An optical storage media consists of a flat, round, portable metal disc, which is coated with a thin
metal or plastic or other material that is highly reflective. These discs usually are 7.5 inches in
diameter and less than one-twentieth of an inch thick.

The information on the optical disk is stored in the form of pits and lands. The pits are the tiny
reflective bumps that are created with laser beam. The lands are flat areas separating the pits. A land
reflects the laser light, which is read as binary digit 1. A pit absorbs or scatters light, which is read as
binary digit 0. The high-powered laser beam creates the pits. A lower-powered laser light reads data
from the disc. Like tracks on a magnetic disk, the tracks of an optical disk are divided into sectors but
shape of these sectors is different than sectors of magnetic disk.

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The operating system assigns a letter to the optical storage devices that come after all the hard disks
and other portable disks. For example, if a computer has one floppy drive, one hard disk, one Zip
disk drive and one CD-ROM drive then letters assigned to drives will be as under:

● 'A and B' for floppy disk drive

● 'C' for Hard disk drive

● 'D' for zip disk drive

● 'E' for CD-ROM drive

The different types of commonly used storage devices are described below:

a. CD-ROM-R or R/W: CD-ROM stands for Compact Disc Read-Only-Memory. CD-ROM is a
type of optical disc that uses laser technology to store and to read
data to and from the disc. A large amount of data can be stored
on a single disk. Once the information is stored on the CD-ROM,
it becomes permanent and cannot be changed (altered). The
information can only be read for processing. Therefore, it is called
Compact Disc Read Only Memory.

Now-a-days, CDs are commonly used in personal computers.
The CD-ROM is removable and can be used to transfer data from
one computer to another like a floppy disk. The storage capacity
of CD-ROM is 1000 times greater than floppy disk. A typical CD-
ROM has storage capacity which is in Mega Bytes from 250, 650,700 MB to 1GB. The software is
available on the CDs. The software companies distribute their products on the CDs. The CD can
be CD-R which is used for read and write multiple times up to the storage capacity. And the
CD-R/W can be used for read, write, and erase multiple times whenever it is needed. For CD-R
and CD-RW needs CD-R drive and CD-R/W drive For example, Microsoft Office and Windows
operating system are available on CDs.

The CD-ROM drive is used with computer to read the
information from the CD-ROM. The data transfer rate of first CD-
ROM used with computer was 150 KBps (Kilobytes per second).
It was known as single speed drive and is denoted by X. This rate
is much slower than that of a typical hard disk drive that reads
data at a rate of 5 to 15 MBps (Megabytes per second).
Manufacturers measure the speed of all CD ROM drive relative
to the first CD-ROM drive. Today, CD-ROM drives have transfer
rates (or speeds) ranging from 48X to 75X or more. For example, a 48X CD-ROM drive has a
data transfer rate of 7,200KBps (i.e. 48 x 150 = 7200) or 7.2 MBps. It. means that the higher the
number, the faster the CD-ROM drive. However, the faster CD-ROM drives are more
expensive.

b. DVD-R or R/W: DVD stands, for Digital Video Disc or Digital Versatile Disc. DVD-ROM is an
extremely high capacity optical disc with storage capacity from 4.7 GB to 17 GB. DVD disc is
specially used to store movie films. It is also used to store huge databases, music, complex
software etc.

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Figure: 1.23 Processor

The latest generation of DVD-ROM disks actually uses layers of data tracks; it is because the
storage capacity of DVD-ROM is very high. The DVD-ROM drive or DVD player reads data
from the first layer, and then look through it to read data from second layer and so on.
Some DVD-ROMs are double sided. It means data is stored on both sides of the disc. A DVD-
ROM looks like a CD-ROM. Although the size and shape is similar to CD-ROM, but DVD-ROM
stores information in different manner A DVD-ROM drive can read ordinary CD-ROM disks.
Its read, write, and erase is similar to CD. It is more qualitative then CD.

Blu-ray Disc

Blu-ray also known as Blu-ray Disc (BD), is the name of a new optical disc format jointly developed by the
Blu-ray Disc Association (BDA), a group of the world's leading consumer
electronics, personal computer and media manufacturers (including Apple,
Dell, Hitachi, HP, JVC, LG, Mitsubishi, Panasonic, Pioneer, Philips, Samsung,
Sharp, Sony, TDK and Thomson). The format was developed to enable
recording, rewriting and playback of high-definition video (HD), means 1080p
resolution as well as storing large amounts of data. The format offers more
than five times the storage capacity of traditional DVDs and can hold up to
25GB on a single-layer disc and 50GB on a dual-layer disc. This extra capacity
combined with the use of advanced video and audio codecs will offer consumers an unprecedented HD
experience.

It uses blue-violet laser beam to read and write data on the disc, hence the name Blu-ray. The benefit of
using a blue-violet laser (405nm) is that it has a shorter wavelength than a red laser (650nm), which makes
it possible to focus the laser spot with even greater precision. This allows data to be packed more tightly
and stored in less space, so it's possible to fit more data on the disc even though it's the same size as a
CD/DVD. Generally its storage capacity is 25GB but when the number of layer is increase the storage
capacity will be 50GB (2 layers) to 500GB on a single disc by using 20 layers. It holds over 9 hours of high-
definition (HD) video and about 23 hours of standard-definition (SD) video on a 50GB disc. Its size is same
size of standard CDs and DVDs.

External Storage Devices

The storage devices which can be connected to the system externally are called external storage devices. It
is not necessary to connect them within the system. External devices can be connected and detached
whenever necessary. These devices are generally used as back up and portable storage media. Portable
devices are generally small in size and cheaper, but they have high storage capacity. They are as fast as
internal or fixed memory.

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Some of the commonly used external devices are flash memory, smart cards, portable hard disks, i-pods
etc. Because of these portable devices, mobile computing has also becoming popular among the mobile
users. Online storage, smart cards, flash memory etc are becoming common as mobile storage devices as
well. Some of the common external storage devices or media are described here.

Online Storage

Online storage is a website on the Internet that offers the storage of data for free of cost or against some
payment through credit card. The capacity of storage depends upon the packages offered by the website
owner. Through the website, data is stored on a computer which remains online 24 hours a day and 7 days
a week.

When you connect to the website, you can browse through your allocated memory space just as you
browse with the help of Windows Explorer on your personal computer. Thus you can access your
data/information wherever you travel throughout the world. National or international travelers having
laptops or handheld computers mostly enjoy the online storage facilities. Many companies offer online
storage facilities such as www.webdepositbox.com is a famous online storage service that allows users to
store, access, and organize files. Even all the e-mail id provider provides some space so we can store the
important documents in the e-mail itself.

Smart Cards

A smart card is a small card normally of the size of credit card or ATM card or even smaller than that. We
can store data/information in the card and sometimes miner
processing of data/information can also be made by its built-in
microprocessor. In order to read and write data on a smart card, a
special device called smart card reader is needed.

There are two types of smart cards:

1. Intelligent Smart card

2. Memory Smart card

An Intelligent Smart card contains a built-in microprocessor and has input, processing, output, and
storage facilities. Whereas a Memory Smart card gives only data storage facility. Many digital cameras,
mobile phones, laptops and handheld computers nowadays use smart cards.

Flash Memory

It is a kind of EEPROM that uses circuit wiring to erase the entire chip or predetermined sections of the
chip called blocks, by applying an electrical field. Flash memory
works much faster than traditional EEPROMs because it writes
data in chunks, usually 512 bytes in size, instead of 1 byte at a
time. The data stored on it can be erased in a flash (whole once).
Today’s most of the data traveler memory is flash memory. It
does not require a battery (electric power) to maintain its
contents.

Flash memory is a type of non-volatile memory that can be erased electronically and reprogrammed,
similar to EEPROM. Most of the PCs also use flash memory to hold their startup instructions. Flash
memory is also known as Flash ROM.

Flash memory chips are also used in mobile computers and devices to store data and programs. For
example, these are used in PDAs, digital cellular telephones, set-top boxes, digital voice recorders, pagers
etc. The flash memory chip in a digital cellular telephone stores names and telephone numbers. The flash

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memory is also used in digital camera. When we take pictures with digital camera, these are stored in a
flash memory rather than on photographic film. Flash memory, commonly known as Pen drive by PC
users, has become common as portable storage.
Similarly, the following devices are also used as external storage;
● Portable Hard Disk: It is same as fixed hard disk, and has same capacity and speed.
● Zip Disk

Memo stick

Memory stick is a portable digital flash memory storage device
used with handheld devices (digital cameras and camcorder). It
is a one of the type of memory card. The storage capacity of
Memory Sticks ranges in size from 4 MB to 256 GB, with a
theoretical maximum capacity of 2 TB. Memory Sticks were first
introduced by Sony in 1998 in their cameras, camcorders and
other digital photography equipment. Generally it is used in
portable digital device.

INPUT AND OUTPUT DEVICES

The input-output or I/O devices provide the means of communication between the computer and the
user. The input and output devices are the hardware components that allow the user to input data and
instructions into the computer and to receive the processed data as information. The data and instructions
are given to the computer through input device. The computer processes the data according to the given
instructions and output is received onto the output device or it is stored permanently on the storage
device.
Various types of input/output devices are available. The I/O devices are slower as compare to the speed
of CPU and memory. It is because the speed of I/O devices depends upon the mechanical movement of
the components of the devices. It is impossible that the I/O devices, the CPU and primary storage have the
same speed.

Input Devices

The devices that are used to enter data and instructions into the computer are called input devices. In old
computers, the punched card readers, paper tape readers were used as input devices. Now-a-days the
most commonly used input devices are Keyboard and Mouse.
Input is any data or instructions entered into the computer in the form of signals. The input into the
computer can be entered:
● Through keyboard (by typing characters).
● By selecting commands (icons) on the screen and then clicking with mouse.
● By pressing finger on a touch screen.
● By speaking into a microphone.
● By sending image through digital camera.
● By scanning data printed on paper through scanner etc.

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Therefore, the devices that are used to enter data and instructions or commands into the computer are
called input devices or units. The input devices are the eyes and ears of computers. The commonly used
input devices are:

● Keyboard ● Digital Camera
● Mouse ● Microphone
● Touchpad ● Digitizer
● Trackball ● Stylus and Curser
● Joystick ● Optical Readers
● Light Pen ● MICR
● Digital Scanner

Keyboard

The keyboard is the most commonly used input device. It is used to feed data and instructions into a
computer. It is similar to an electric typewriter. A keyboard contains keys for each alphabetic characters,
digits and special characters. The data and instructions
are feed into the computer by pressing the related keys
on the keyboard. The keyboard has some additional
keys for specific functions. Keyboard used with personal
computer typically have from 101 to 105 keys, and this
type of keyboard is called enhanced keyboard. The
original PC keyboard and AT keyboard has 84 keys.
These three types of keyboards differ somewhat in the location of function keys, control keys, enter key,
and the shift key etc.

On laptop and many other handheld computers, the keyboard is built into the top of the system unit.
Usually, these keyboards are smaller in size and have fewer keys such as 84 keys.

Some earlier computers have built-in keyboards. Now-a-days, the computer has a separate keyboard. It is
easily plugged in computer. A keyboard is connected to the serial or USB port on the system unit. A
standard computer keyboard is also referred to as QWERTY keyboard. This name represents the first left
most letter on the top alphabetic line of the keyboard spell. Some advanced keyboards do not require the
cable to connect with the cable. They enter data into the computer through wireless technologies such as
radio waves or infrared light waves. These types of keyboards are known as cordless or wireless
keyboards.

Division of Keyboard

A keyboard cab be divided into four areas, which are described below.

1. Alphanumeric Keypad: This area is like a typewriter key, it is because this area of keyboard is
referred to as Typewriter Area. The user uses this area to enter general information into the computer.
Typists usually use this area of keyboard. This area consists of;

● Alphabetic character keys "A" to "Z" and lower case letters "a" to "z".

● Numeric keys "0" to "9".

● Many other special keys like Spacebar, Enter key, Ctrl key etc.

2. Numeric Keypad: A set of numeric keys and arithmetic operator keys on the right of keyboard that
are similar to calculator keys is referred to as Numeric Keypad. It also has an extra Enter key and
Num Lock key. The Num Lock key is used to activate or deactivate the numeric keypad. The numeric
keypad is mostly used for numeric data entry.

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3. Screen Navigation Keys: The keys that are normally used in word processor or other application
programs to move cursor into the document on the screen are referred to as navigation keys. The
most important navigation keys are: Arrow Keys, Page Up Key, Page Down key, End Key, and Home
Key.

4. Editing Keys: The keys that are normally used in word processor or other application programs for
editing (modifying) the document are referred to as editing keys. The most important editing keys
are: Delete Key, Backspace Key, Enter Key, Tab Key, Caps Lock Key, Insert Key.

5. Function Keys: There are 10 or 12 function keys on the top of keyboard that are labeled as F1, F2,...
F12. These keys are referred to as Function Keys. These are used to perform special functions. The
function of each key depends upon the software being used on the computer. The designer of the
software assigns these keys in his software as shortcut commands or keys to perform specific task.
For example, in most software the function key F1 is used to get online help about the software
running on the computer.
The advanced keyboards also include buttons that allow the user to access the computer's CD or
DVD drive. Adjust speaker volume, open an e-mail program, start a web browser and search the
Internet. Some keyboards also provide the USB ports used to plug the USB device directly to the
keyboard instead of system unit.

Mouse

Mouse is a pointing input device. It is the most commonly used
pointing device in Windows environment on the personal computers.
The mouse has two or three buttons on the top of its body. Mouse is
used to select any option from a group of options by pointing the
mouse pointer on it and then clicking one of the mouse buttons.
A mouse also allows the user to create graphics such as lines, curves
and freehand shape on the screen. The graphic designer cannot draw
graphs without mouse. A mouse is connected to a serial port or USB
port on the system unit. The most popular types of mouse and their
functions are:

1. Mechanical Mouse: It has a rubber or metal ball at its bottom and an electronic circuit containing
sensors. Whenever the mouse is rolled over a flat surface; the pointer moves in the same direction as
of mouse. The sensors detect the direction of movement of ball and electronic circuit translates the
movement of the mouse into signals and then feeds it as input in the computer.

2. Optical Mouse: It has advance features and is more expensive than mechanical mouse. It has no ball
inside it. It uses the laser technology to detect the mouse movement by optical sensors. Mouse may
be cordless (wireless). It means mouse is not directly connected with computer. It uses the wireless
technology, such as radio waves or infrared light waves. It enters input signals into the computer in
similar fashion as cordless keyboard.

3. Opto-mechanical Mouse: It is same as mechanical mouse, but uses optical sensors to detect motion
of the ball.

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Trackball

A trackball is also a pointing input device. It is like a mouse, but it is a stationary pointing device with a
ball on its top. It is a hard box with a rolling ball at the top and one or
more buttons that work just like mouse. The ball is rolled or rotated
with finger to move the cursor or pointer around the screen. Like
mouse, specific item is selected by pointing with trackball and then
pressing with one of the buttons. The trackball is usually available
with laptop computers and is fixed on the keyboard.

Some cordless trackball are also available. They are not directly
connected to the computer with wire, and acts like a remote control
for the pointer. They are especially useful when giving presentations
because the presenter often walks around the room instead of sitting
at a computer.

Touchpad

A touchpad is also known as track pad. It is small, flat, rectangular stationary pointing device. It has
sensitive surface of 1.5 or 2 inches square. To move the
pointer, slide finger tips across the surface of the pad.

Some touchpad have one or more buttons around the
edge of the pad that work like mouse buttons. The
touchpad pointing device is mostly used in laptop
computers and is built-in on the keyboard. You can also
attach a track pad to a personal computer. The advanced
keyboards also have built-in track pad.

Joystick

Joystick is also a directional pointing input device. It has small box with a
moving handheld stick and buttons like gear of a vehicle. The handheld
stick is used to control the movement of pointer on the screen. The button
of the joystick is pressed to activate certain events. The joystick input
device is used to play games. It is also used with simulation software in
education fields.

Light Pen

Light pen is another pointing input device. It can detect the presence of light. It is a handheld pen shaped
device with a photocell mounted at its front end. When the front end of the
pen is touched with the monitor screen, the photocell detects or senses a
position of display screen. This device also has button. The user points the
object to be selected on the screen with light pen and then presses the
button on the pen. Light pen devices are used by engineers, graphic
designers etc. These devices require special monitors. Light pen is used in
Personal Digital Assistant and other types of handheld computers.

The electric light pen input device is generally used with designing
software. In designing display screen data can be entered with a light pen
by pointing the screen positions. A spot appears on the display screen at
the location where pen is touched and it is sensed by the light sensitive photocell detector. The computer
program controls the input signal of this device.

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Digitizer

A Digitizer is also known as Graphic Tablets. It is a flat, rectangular electronic plastic board (or pad). Each
location on the digitizer points to corresponding computer screen. It
is mainly used for making maps and engineering drawings. The
input devices stylus and puck (or cursor) is used to trace drawings
and sketches on the digitizer.

When we draw on digitizer with the help of a stylus or cursor, it
converts the movements of stylus or cursor into digital signals that
are later sent into the computer. Thus, digitizer makes it easy to enter
free-hand drawing in the computer.

Microphone

Microphone is an input device used to enter the sound signals of user into the computer. It is used to
record the voice of the user in a computer. It is also used to talk to
others on the Internet. For this purpose, it is necessary to have the
microphone and a sound card with the computer.
The sound card translates the sound signals (analog) into digital
signals for processing by computer. The sound card can also translate
the sound digital signals back into analog signals and then sent to the
speaker. Some computers have the capability of understanding
spoken words and thus data can be entered with the help of
microphone. Such facility is called Voice Recognition. Voice
recognition software uses a database of already entered spoken
words. This database is used to recognize the words spoken by a
computer user. A user, therefore, thinks that the computer
understands whatever he speaks on.

Today, microphone is becoming important as input device to record speech. Most personal computers
now have phone-dialing capabilities, if we have a microphone with an earphone, we can communicate
with others through personal computer. We can also use a microphone to record our voice and can store it
in a file on disk. This file can be sent by e-mail to others. Microphone can be clip mic., stand mic. or built in
with the earphone.

Digital Camera

Digital Camera is an input device used to take pictures and to store
directly in computer in digital form. It operates on the same basic
principle as a traditional or conventional camera but digital camera
sends images directly inside the PC in digital form instead of storing
it on a conventional film.

When a picture is taken with digital camera, the electric image of the
picture is stored in digital form on the floppy disk or CD-R attached
with the camera. The stored picture can be loaded into the computer
from the disk for editing. Digital cameras can differ in resolution, and
higher the resolution, higher the quality of picture. But, the high
resolution picture occupies more memory space.

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Digital Scanner

Digital scanner is a very popular input device. It is a light-sensing input
device. It reads images and text printed on the paper, and then translates
into electronic form that can be processed and stored by the computer. The
scanner is also known as image scanner. The Scanner uses the laser
technology to scan the image of the printed paper and store it into the
computer. Once an image is scanned, it can be used for following purposes.

● Can be stored in a disk for future use.

● Can be printed on the paper.

● Can be attached to an e-mail message etc.

● Can be transferred to the paint program for processing or it can be directly opened in the word
processing program for editing.

The software is used to manipulate the scanned image. For example, if we have scanned text document
then we might have to use optical character recognition (OCR) software to translate the image into text for
editing. Similarly, if we have scanned a photo then we might have to use the Adobe Photoshop graphic
software to adjust its colors, size etc.

Magnetic-Ink Character Recognition (MICR)

MICR is similar to OCR but used magnetic instead of optical. It is used by banking organization for faster
processing of large volume of cheques handled every day. A bank has
cheques containing magnetic strip of bank’s identification code (name,
branch, branch code, etc), account number and cheque number pre-printed
by special ink (magnetic ink) containing magnetic particles (iron oxide) on
it by using characters from a special character set. MICR is a direct entry
method in banks. It is used to automatically read numbers on cheque.

Optical Readers

An optical reader is a device that uses a light source to read characters,
marks printed on the paper etc. and then converts them into digital form
that can be stored and processed in computer. These devices are similar to
digital scanners. There are three main types of optical readers.

1. Bar Code Reader (BCR)

2. Optical Character Reader (Recognition)

3. Optical Mark Reader (OMR)

1. Bar Code Readers: Data coded in the form of light and dark lines or
bars are known as bar codes. The bar codes are particularly used for
labeling products (or goods) and books in public libraries. The code
number on the product or book is represented by a pattern of vertical
bars. The most widely used bar code is the Universal Product Code
(UPC).

Bar-Code Reader is an input device used for reading (or decoding) bar
codes on the product or book. The most common type of bar code
reader is the flatbed model, which is commonly used in super markets
and departmental stores. The bar code reader reads the bar code

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printed on the product and converts into a code the computer can understand. The bar-code reader
contains the photoelectric cell or light- sensitive detector that reads the bar code by means of reflected
light. The bar-code reader emits a laser beam of light that is reflected by a bar code pattern. The bar-
code reader decodes the bar code and then records into computer as input data.

2. Optical Character Recognition (OCR): The OCR devices (or scanners) are used to scan special
characters (such as alphabetic and numeric characters)
printed on the paper and fed into the computer as input
data. The OCR device also uses a light source to read the
characters printed on the paper. The characters printed on
paper may be typewritten or handwritten. In case of
handwritten, the characters must be of standard size but in
case of typewritten, the characters must have the special
type font called an OCR font. The accepted OCR fonts are
OCR-A (American standard) and OCR-B (European
standard).

The OCR software is used to translate the scanned image of text document into text. When OCR
device creates an image from a page, the image is stored in the computer’s memory as a bitmap. A
bitmap is a grid or array of dots and each dot is represented in memory by one or more bits. The
OCR software translates the array of dots into text or number. The characters that match with the
standard OCR fonts are stored into the computer and others are rejected. The scanned text document
can be edited with the help of word processor. OCR devices are expensive and are used by credit
card companies, large businesses for following purposes.

● to read postal zip code.

● to read passenger tickets and freight bills by airlines.

● to process special security forms.

● to monitor vehicle registrations by governments.

3. Optical Mark Reader (OMR): The scanner is capable of recognizing a pre-specified type of mark
made by pencil or pen. The actual technique used by an
OMR device for recognition of marks involves focusing a
light on the page being scanned and detecting the reflected
light pattern from the marks. Pencil marks made with a soft
lead pencil (high graphite content) reflect the light enabling
the reader to determine which response is marked. For
example, Objective type choices of correct answer on a
special pre-printed test scoring sheet by darkening a small square, circular, or oval shaped box by a
pencil are read by OMR.

Output Devices

The processed input data into a useful form is called output. The computer processes the given input data
and gives the output. Therefore, devices that are used to get output from a computer in readable form are
called output devices. When input data is processed, computer generates several types of output,
depending upon the hardware and software used and the requirements of the user. The user views output
on a screen print it on the printer or hear it through speakers or headsets.

A number of output devices are available. Some commonly used output devices are video display units
(VDU) and printers. Output is normally classified as:

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1. Softcopy Output Device

2. Hardcopy Output Device

Softcopy Output Device

The output received on the display screen or in the audio or video form is called softcopy output. It is
stored in computer. This kind of output is not tangible and it cannot be touched. The most popular and
commonly used softcopy output device is display screen. The output received from the speakers in the
form of sound is also an example of soft copy output and is called sound output. It is a kind of temporary
output, as we need power supply and display screen continuously for uninterrupted output. It is useful
for text, graphics, audio, video or animation etc.

Monitors

The monitor is a popular and most commonly used output device. The monitor consists of a screen and
the electronic components that produce the output on the screen temporarily. The output received on the
screen is called softcopy output. Most monitors used in personal computers display text, graphics and
video information. Monitors can be divided into following categories.
1. Monochrome monitors: Monochrome means information displays in two colors, one color (such as

white, green, black, blue, amber or gray) for fore ground and one color for background, which is
usually black. These monitors are usually used to display text only where you don’t need to see color
graphics. Some PDAs and other mobile devices use monochrome monitors to save battery power.
2. Grayscale Monitors: Grayscale monitors are types of monochrome monitors. These monitors often
use gray scaling to enhance the quality of graphics. They display the output using many shades of
gray from white to black, which provide better contrast on the images. They are also used in
handheld computers.
3. Color monitors: Color monitors are used to display output in different colors (i.e. from 16 colors to
16.7 million colors). These monitors are sometimes called RGB (Red, Green, Blue) monitors. The color
and gray scale monitors are often classified by the number of bits they use to represent each pixel.
For example, an 8-bit monitor represents each pixel with 8 bits. Today, most of the personal
computers use color monitors.
Types of Monitors
These are types of monitors that are used with personal computer:
1. CRT Monitors
2. Flat-Panel Monitors (LCD)
3. Touch Screen Monitors
4. LED Monitors
5. Plasma Monitors
1. CRT Monitors: A CRT monitor is similar to standard television. It contains a cathode ray tube (CRT).
A cathode ray tube is a large, scaled glass tube. The front of the tube is the screen. The back of the
screen is coated with phosphor (chemical material that glows when electron beam falls on it). The
screen is organized into a grid of tiny dots of phosphor material. Each dot consists of a red, a green
and a blue phosphor. The smallest number of phosphor dots that the gun can focus on is called a
pixel (short for picture element). A pixel indicates a single point in an electronic image.

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CRT monitor contains an electronic gun. The electronic gun shoots a beam of electrons through a
magnetic coil and moves back and forth across the back of the
screen. This causes the dots of phosphor on the screen to glow,
which produces an image on the screen. The electron beam
scans each line of pixels across the screen until it reaches the
bottom of the screen and then it starts over.

Today, most of the PCs have color monitors. A color monitor
works like a monochrome one, except it contains three electron
guns; one for red color, second for green color and third for blue
color.

In a color monitor, each pixel includes three phosphor tiny dots.
These are red, green and blue arranged in a triangle. When the
beams of each gun are combined and focused on a pixel, the
phosphors light up. The output is displayed in different colors
by combining various intensities of the three guns. A typical monitor can display output in 256 to
65,536 colors.

Like televisions, CRT monitor size is measured diagonally, in inches, across the front of the screen.
For example, a 17-inch monitor measures 17 inches from the lower left to the upper right corner. CRT
monitors are available in various sizes, i.e., 15, 17, 19, 21 and 22 inches etc. The large size monitors are
more expensive, but allow to view more information on the screen at once.

2. Flat Panel Monitors: A flat panel monitor is also called LCD monitor. It uses a liquid crystal display
(LCD) instead of a cathode ray tube to produce output on the screen.
The LCD uses a liquid compound to display information on a screen.
Typically, LCD has fluorescent tubes that emit light waves toward the
liquid crystal cells, which are sandwiched between two sheets of
material. When an electrical charge passes through the cells, the cells
twist. This twisting causes some light waves to be blocked (while
others are passed through) and creating image on the screen. LCD
monitors are 40% more efficient than older CRT monitors.

A flat panel monitor takes up less desk space and also consumes less
power. Flat panel monitors are available with different sizes such as
15, 17, 18, 20, 21 and 23 inches. Flat panel monitors are commonly used
in mobile devices such as laptop and tablet PCs. Similarly, smart phones, PDAs calculators have LCD
screens. E-book is another mobile device that use LCD screen. The standard size of panel monitors
for laptop computers is 15 or 16 inches. There are two main categories of LCDs. These are:

i. Active Matrix LCD

Active matrix LCD uses a transistor for each liquid crystal cell or pixel and thus displays high
quality images. Active Matrix LCD is also known as Thin Film Transistor (TFT) display. Today,
new generation of TFT is called Organic LED that displays brighter images than standard TFT
display. The organic LED uses organic molecules to generate output on the screen.

ii. Passive Matrix LCD

Passive matrix LCD uses fewer transistors and requires less power than active matrix LCD. The
colors on passive matrix LCD are not bright as compared to active matrix LCD.

The quality of LCD screen depends on its resolution, which is general proportional to the size of
screen. For example, a 15 inch flat panel monitor typically has a resolution of 1024 x 768, while a
17-inch has a resolution of 1280 x 1024.

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3. Touch Screen Monitors: These are special monitors through which input data is directly entered by

touching the screen with user fingertip. Usually, it is used to make
selection from a menu of choices. Most touch screen computers use
sensors in the computer’s screen to detect the touch of a finger.
Automated Teller Machines (ATM) interface is an example of touch
screen.
In some computer systems, pen-based or light pen input devices are
used. The user touches the screen with a pen. However, the term
touch screen implies a system that accepts input data by touching the
screen with the user’s fingertip. Touch screen systems are used in
restaurants, supermarkets, departmental stores etc. Most PDAs,
Laptop, and Tablet PCs also have touch screens.
4. Light Emitting Diode (LED) Monitor: This type of screen is composed of light-emitting diodes. Its
name comes from the English Light Emitting Diode. Light emitting diodes are the most popular tool
for lighting liquid crystal displays nowadays. Light emitting diodes consume a little electricity, retain
a low temperature even after long hours of performance, and endure high loads. That’s why such
displays are used as TV screens and monitors for computers. LED displays are a kind of displays that
feature light emitting diodes to highlight the screen. They are normally located around the edges of
the panel or behind the crystals, highlighting the matrix. The picture created with the help of this
technique is very bright and vibrant. Besides that, black hues are incredibly deep and dark. Thanks to
the diode highlighting, the picture is as realistic as possible. LED monitors offer 20% energy
efficiency compared to LCD monitors, which qualifier them with energy star certified. The minimum
resolution of these monitors is 1224 × 768.
5. Plasma Monitor: It is a type of flat panel display that utilizes small cells containing electrically
charged ionized gas. A plasma display is a computer video display in which each pixel on the screen
is illuminated by a tiny bit of plasma or charged gas, somewhat like a tiny neon light.
Plasma displays are thinner than cathode ray tube (CRT) displays and brighter than liquid crystal
displays (LCD). It has better picture quality and less energy saving as well as usually available in
large size.

Figure: 1.24 Plasma monitor

●

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Difference between CRT and LCD Monitor

CRT LCD

1. Uses vacuum tube and electron guns. 1. Uses Liquid Crystal.

2. Light glow while striking electron on a 2. While supplying electricity, crystal becomes

coated surface of phosphor transparent.

3. Emit radiation. 3. No radiation emitted.

4. Harmful for the eyes. 4. Not harmful for eyes.

5. Picture quality is high. 5. Picture quality is low.

6. Viewing angle is large. 6. Viewing angle is very small.

7. Cost is low. 7. Cost is high.

8. Occupy large space. 8. Occupy small space.

9. High power consumption. 9. Low power consumption.

10. Screen size is not exact of its given size. 10. Screen size is about to mention size.

11. Screen is flicking 11. No flicking.

12. Resolution can be changed according to our 12. Better to keep the default resolution.
need frequently.

13. Old technology. 13. New technology.

Speakers

Speaker is an electro-acoustic transducer that converts electrical signals into sounds loud enough to be
heard at a distance. Speakers are soft copy output
devices that can be used to produce sound as output. In
order to produce sound output through speaker, a
sound card is necessary. The sound card also helps to
record sound input from a microphone, and manipulate
sound stored on a disk. Speakers can be used to produce
mono, stereo or 3D sound.

Computer speakers are also called multimedia speakers.
They often have a low-power internal amplifier. The
standard audio connection is a 3.175mm (1/8 inch) stereo jack plug often color coded (lime green) for
computer sound cards. Computer speakers range widely in quality and in price. The computer speakers
typically packaged with computer systems are small plastic boxes with mediocre sound quality. Some of
the slightly better computer speakers have equalization features such as bass and treble controls,
improving their sound quality somewhat.

Hardcopy Output Device

The output printed on the paper is called hardcopy. The printers and plotters devices are used for this
purpose. The hard copy output can be stored or transported by the user in paper form. Hard copy output
is useful, especially when there is no provision of soft copy output, computer or power supply. It is a kind
of permanent output.

An output device is a hardware component used to get output from the computer. A number of output
devices are available. The commonly used output devices include display device (monitor), printer,
speaker and headset, fax machine etc. It is useful especially for text and graphics, and it can't be used for
audio, video or animation etc.

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Figure: 1.25 Hard copy output devices

Hard Copy Output Devices

Printers Plotters

Impact Non-Impact Flatbed Drum

Dot Matrix Daisy wheel Line Laser Ink Jet Thermal

Printers and Plotters
People often prefer to get printouts of the work they have done rather than to look at it on the screen.
Printouts are called hard copy output. Unlike images on a screen, hard copy can provide a permanent
record of work and can be looked at away from the computer. Hard copy can be obtained using a printer
or a plotter. There are different types of printers and plotters available. They vary in the method they use
to produce hard copy and the cost and the quality of the hard copy they produce. Different devices are
suitable for different applications.

Printer

Printers are usually divided into two different categories:

1. Impact Printer

2. Non-Impact Printer.

This is a "family tree" of output devices that can produce hard copy:

1. Impact Printers: Impact printers produce output by striking a ribbon with a hammer. When the
ribbon is hit, a mark is made on the paper behind it. If carbon paper is put into the printer then an
impact printer can print more than one copy of a document at a time. This feature is often used by
companies when they print invoices, bills etc. Because of the hammering action, impact printers are
noisy when they are printing. Printing technology is old and slow as compare to non-impact printer.
Cost and quality is also comparatively less than non-impact printer. The different types of impact
printers are described below.

a. Dot Matrix Printers: Dot matrix printers produce an image by hammering a column of 9 or 24
pins against a ribbon. Characters are produced as the print head (which contains the pins)
moves across the page. It is called Dot Matrix because it prints the character with the
combination of dots. Dot Matrix printer prints in both directions. This is very old printing
technology, but it is popular in most of the billing departments.

Figure: 1.26 Dot matrix printer

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Dot matrix printers are costly to purchase, but have low operating costs. Most of them can run
in either draft mode (quick but very low quality) or Near Letter Quality mode (slower but better
quality). The disadvantages of dot matrix printers are that the output quality is poor, it takes a
long time to print a document and the noise can be annoying. The speed of dot matrix printer is
measured in characters per second (cps). The slowest dot matrix printers create 50-70 cps, the
fastest print more than 500 cps.

b. Daisy Wheel Printers: Daisy wheel printers are rarely used any
more. A daisy wheel printer hammers character stamps (like
those on typewriters) against a ribbon to produce high quality
text output. The character patterns are all arranged around the
edge of a wheel. When a letter is to be printed, the wheel rotates
so that the correct letter is against the ribbon. A hammer then
hits the letter against the ribbon to print it on the paper. Daisy
wheel printers are very slow and noisy. It is not possible to print
graphics using a daisy wheel printer. It is not flexible to print
different size of character, if then, need to change the wheel and
hammer head. Its printing speed is 10 to 75 characters per second.

c. Line Printers: Dot matrix and daisy wheel printers both print only one character at a time. For
that reason they are called Character Printers. In contrast, a line printer prints a whole line
(typically 80 or 132 characters) of text at a time. These printers are very fast, the fastest can print
3,000 lines of text per minute. The line printers may be Chain or Drum (Band) type. The
mechanism may use a large spinning print drum or a looped print chain. As the drum or chain
are rotated over the paper's surface, electromechanical hammers behind the paper push the
paper (along with a ribbon) onto the surface of the drum or chain, marking the paper with the
shape of the character on the drum or chain. They are expensive to buy and are used when high
volumes of output are required. Example applications include printing telephone bills or bank
statements.

Figure: 1.27 Chain printer Figure: 1.28 Drum printer

2. Non-Impact Printers: Non-impact printers do not use hammering action. Because there is no
hammering action, non-impact printers are very quiet but cannot print multiple copies using carbon
paper. Printing quality and speed is better than the Impact printer. This type of printers can be used
in any organization. The cost of printers are varies from low to high according to its quality and
manufacturing company. It is a present mostly used printing technology. The non-impact printers
can be Inkjet, Laser, and Thermal.

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a. Ink Jet Printers: An Inkjet printer uses one of the most popular printing technologies today.
The relatively low cost of the printers and multi-purpose printing
abilities make it a good choice for small businesses and home
offices. Inkjet printers turn images or text by spraying tiny
droplets of ink over the paper, through the precisely controlled
number of nozzle and sophisticated controlled mechanism. They
produce moderate quality printouts and are cheap and less noisy.

Typically, ink jet printers can produce 360 or 720 dots per inch
(dpi) but these dots are larger than those that a laser printer
makes. So the quality although very good is not quite as perfect.
Ink-jet printers can work in black and white or color. They are
slower than laser printers (3 ppm) and cost slightly more to run.

b. Laser Printers: Laser printers are called Page Printers because they print a whole page at a
time. Laser printer operates in the similar manner as a photocopy
machine. A laser beam is used to draw the image to be printed
onto a light sensitive Drum. After the image has been drawn on
the drum a fine dust like powder ink called Toner is put onto it.
The toner only sticks where the laser has drawn the image. The
paper then passes over the drum and the toner is transferred onto
the paper.

Laser printers are often deployed in enterprises as a workgroup
or departmental print center, where performance, durability, and
output requirements are a constant. Typical home laser printers
can print 8 pages per minute (ppm). Some industrial versions
print over 40 ppm and can print on both sides of paper at the same time. The main
disadvantage of this type of printer is the high cost. Running costs are higher than impact
printers but lower than most ink jet printers. They are relatively expensive but have following
advantages.

1. Very high speed.

2. Low noise

3. Low maintenance cost.

4. High image and excellent graphics quality.

c. Thermal Printers: Thermal printers are no longer used as printers for PCs. They are, however,
still used in some computer control systems, calculators and in
many fax machines. These printers print on special heat sensitive
paper which is expensive. The image is produced from small dots
which are made on the paper by heating it up. They produce low
quality print, and the paper tends to curl and fade after a few
weeks or months. Thermal printers are in, but expensive, but can
print graphics as well. The output produced by these printers is
said to be either letter quality, near letter quality, draft quality, or
image quality. This print is obtained from the one minute photo
camera.

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Difference between Impact and Non-Impact printer

Impact Printer Non-Impact Printer

1. Impact printer prints by striking hammer head 1. Non-impact printer prints without striking on
over the ink ribbon on a paper. a paper.

2. This printing technology is a 2. Printing technology may be thermal,
electromechanical which is becoming obsolete. electrostatic, laser or any other which is
emerging.
3. It is very noisy.
4. Slow in printing. 3. No sound produced while printing.
5. It is a text printer. 4. Printing is fast.
6. It can print multiple copies at a time. 5. Prints text as well as graphics.
7. Print quality and cost is low. 6. It can print single copy at a time.
8. It can print character or line at a time. 7. Print quality and cost are both high.
9. Cost of printer is low.
10. For example, Dot Matrix, Daisy wheel, Line 8. It can print whole page at a time.
9. Cost of printer is high.
etc. 10. For example, Inkjet, Laser, Thermal, etc.

Plotters

A plotter is a specialized output device designed to produce hard copy output of charts, maps, large
drawings, graphs etc. A plotter is a very versatile tool. It is a device that draws pictures on paper based on
commands from a computer. It is sometimes confused with a printer, but plotters differ from printers in
that they draw lines using a pen. As a result, they can produce continuous lines, whereas printers can only
simulate lines by printing a closely spaced series of dots. Multi-colored plotters use different colored pens,
and can automatically change their pens to draw different colors. It is very expensive, large and slow.

A plotter can be used to produce very large drawings on paper sizes up to A0 (16 times as big as A4). The
lines drawn by a plotter are continuous and very accurate. They are usually used for Computer Aided
Design (CAD) and Computer Aided Manufacturing (CAM), and other engineering applications such as
printing out plans for houses or car parts where precision is mandatory. Plotters are very slow but
produce high quality output.

There are three types of plotter. They differ in the way that the pen can be moved about on the piece of
paper to draw lines:

Figure: 1.29 Flatbed Plotter Figure: 1.30 Drum Plotter Figure: 1.31 Electrostatic Plotter

● Flatbed Plotter: The paper is fixed and the pen moves left and right and up and down across the
paper to draw lines. In this, plotter uses more than one pen to draw on a paper.

● Drum Plotter: The pen moves up and down on the paper and the paper is moved left and right by
rotating a drum on which the paper is placed.

● Electrostatic Plotter: There is one more plotter which is technologically different than above two
types, and it is called electrostatic plotter. Electrostatic plotters use electrostatic charges to create
images out of very small dots on specially treated paper.

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COMPUTER PERIPHERALS

Peripheral devices, or simply peripherals, are the computer devices that are connected to the computer
externally such as printer, scanner, keyboard, mouse, tape device, microphone and external modem. Some
of them can be internal such as CD-ROM or internal modem and external as the scanner, printer and Zip
drive. Peripherals are used to communicate with the outside world or hold information over a long period
of time. Peripheral devices can be classified into different types according to their functions or use. The
different types of peripherals are;

● Input devices that are used to feed data and instructions into the computer such as keyboard, mouse,
scanner, microphone, digital camera, track ball, touch pad etc.

● Storage devices which are used to store data for backup like magnetic disks such as hard disk; CD-
ROMs, flash memory, magnetic tape etc.

● Output devices that are used to get the information from the processor or display the result to outside
world; such as, VDU, printers, plotters, speakers etc.

INTERFACES

Interface is a boundary across which two independent systems meet
and interact or communicate with each other. Therefore, it is simply a
point from where the communication can be possible. In computer,
there are different types of interfaces like user interface, software
interface and hardware interface. In this lesson, we will concentrate
on the hardware interface alone.

Hardware interface is the wires, plugs and sockets that hardware
devices use to communicate with each other, and electrical signals
that are passed across them. In short, it is a jack (port) for connecting
different peripheral devices. Input to the system and output from the
system is possible because of the interface. Hardware interfaces exist in computing systems between many
of the components such as the various buses, storage devices, other I/O devices, etc. USB, FireWire,
Ethernet, parallel and serial ports as well as Compact Flash cards, PCI cards and PC Cards are all
examples of hardware interface (devices connecting to other devices).

Serial port

Serial ports are a type of computer interface that complied with the
RS-232 standard. It is serial communication physical interface
through which information is transferred in or out one bit at a time.
Each byte is broken up into a series of eight bits, hence the term serial
port. Serial ports are one of the oldest types of interface standards.
Before internal modems became commonplace, external modems
were connected to computers via serial ports, also known as
communication or "COM" ports. Computer mice and even keyboards
also used serial ports. Some serial ports used 25-pin connectors, but
the 9-pin variety was more common. Serial ports are controlled by a
special chip call a UART (Universal Asynchronous Receiver Transmitter).

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Serial ports can be found in industrial automation systems, scientific analysis, shop till systems and some
industrial and consumer products. Network equipment (such as routers and switches) often has serial
ports for configuration. Serial ports are still used in these areas as they are simple, cheap and allow
interoperability between devices. Data can be transferred up to 3M (10ft) with its best performance. In
traditional computers, serial ports were configured as follows:

Serial ports Interrupt Memory address

COM 1 IRQ 4 0x3f8

COM 2 IRQ 3 0x2f8

COM 3 IRQ 4 0X3E8

Com 4 IRQ 3 0x2e8

Parallel Port

Parallel port is a port on the PC that handles a data stream in a parallel mode. On PCs, the parallel port
uses a 25-pin RS-232 connector (type DB-25) and is used to connect printers, computers and other devices
that need relatively high bandwidth. That is, the data is sent out or received in an 8 bit (one byte) at a time
on 8 lines or connector pins. Other lines or pins are used for handshaking or data transfer control. The
standard IBM-PC parallel port interface is termed a Centronics after the company that designed the
original standard for parallel communication between a computer and printer. So, parallel port was
originally used as a printer interface. Normally this parallel port is used only for output from the PC. Later
versions of the parallel port include bidirectional data transfer. Some computers have more than one
parallel port and are denoted as LPT2, LPT3, etc. Most personal computers have both a parallel port and at
least one serial port.

Figure: 1.32 DB-25 parallel printer port Figure: 1.33 SCSI port socket

A newer type of parallel port, which supports the same connectors as the Centronics interface, is the EPP
(Enhanced Parallel Port) or ECP (Extended Capabilities Port). Both of these parallel ports support bi-
directional communication and transfer rates ten times as fast as the Centronics port. Macintosh computer
uses a SCSI port, which is parallel, but more flexible than centronics port.

Parallel ports transmit one byte at a time by using eight parallel wires that each carry one bit, while the
serial ports transmit only one bit. So, data transfer rate in parallel port is higher than serial port. The
primary factor that affects network printing speed is whether the printer is connected to parallel ports or
serial ports. Parallel ports normally are about two times faster than serial ports at 9,600 baud, and up to
four times faster than serial ports at 4,800 baud. Unless distance requires the use of a serial port, parallel

port is used for best performance. Data can be transferred up to1.8m (6ft) with its best performance.

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Universal Serial Bus (USB)

USB stands for ‘Universal Serial Bus’. A USB port is a standard cable connection interface on personal
computers and consumer electronics that works
universally. USB ports allow stand-alone electronic
devices to be connected via cables to a computer or to
each other. Now, The USB connector ports are
available as standard on virtually every computing
machine manufactured in the past eight years.
USB is an external bus standard that supports data
transfer rate of 12 Mbps. USB also supports plug and play installation. USB has become widespread, and is
expected to completely replace serial and parallel port.
USB currently exists in three standards: 1.0, 1.1, and the high-speed 2.0. The original USB 1.0 was relatively
slow, transferring in 1.5 Mbps. Revision 1.1 USB jumped up to 12 Mbps. ‘High-Speed USB’ or USB 2.0,
now the most common interface around, boasts theoretical speeds of up to 480Mbps. USB 2.0 is a newer
implementation of the USB standard and was jointly developed by Hewlett-Packard, Intel, Lucent,
Microsoft, NEC and Philips.
USB connectivity is easier and easy to manage. USB is the first cross-platform “hot-swappable” interface
having no more operating system incompatibility, no more restarting before unplugging or plugging in,
and no more mess. A USB is the replacement for the PC's serial port which allows up to 127 devices to be
connected using either a hub device or by daisy-chaining.
USB has become an industry standard for short-distance digital data communications. USB ports can also
supply electric power across the cable to devices without their own power source. Both wired and wireless
versions of the USB standard exist, although only the wired version involves USB ports and cables.

IEEE 1394

IEEE 1394 is a personal computer / consumer
electronic serial bus interface standard offering high-
speed communications and asynchronous real-time
data services. The IEEE 1394 standard for the High
Performance Serial Bus defines a serial data transfer
protocol. The capabilities of the 1394 bus are sufficient
to support a variety of high-end digital audio/video
applications, such as consumer audio/video device control and signal routing, home networking,
nonlinear DV editing, and 32-channel (or more) digital audio mixing.

IEEE - 1394 Features
● Real-time data transfer for multimedia applications
● 100 - 200 - 400 - 800 Mbits/s data rates
● Live connection/disconnection without data loss or interruption (hot-plug)
● Automatic configuration supporting "plug and play"
● Freeform network topology allowing mixing branches and daisy-chains
● No separate line terminators required

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.68 … Computer Science–I

● Guaranteed bandwidth assignments for real-time applications
● Common connectors for different devices and applications

IEEE-1394 is based on Apple Computer’s original 1394 bus, which was intended as a low-cost
replacement for or supplement to the SCSI bus that is a standard feature of Macintosh and PowerMac
computers.

Network Interface Cards (NIC)

Network Interface Cards can be a network card,
network adapter, LAN Adapter or NIC (network
interface card). They are a piece of computer hardware
designed to allow computers to communicate over a
computer network. It is used for fault communication
via cable. Data is transmitted over a cable network. The
NIC connects computers and other devices such as
printers. Many modern motherboards have NICs built
in by default. This interface can be wire or wireless.

Personal System 2 (PS/2)

PS/2 ports (now outdated) were for connecting peripherals such as
your keyboard and mouse to the computer. PS/2 based mice and
keyboards have now been replaced by USB ports as the popular
standard. This trend for USB over PS/2 started in circa 2004.

HDMI

It stands for High Definition Multimedia Interface. It is a connector and cable trademark and brand name
for a digital capable of transmitting high-quality and high-bandwidth streams of audio and video between
devices. The HDMI technology is used with devices such as Projector 4K televisions, HDTVs, audio
receivers, DVD and Blu-ray players, cable boxes, and video game consoles.

Because HDMI is a digital connection, HDMI cables are less prone to interference and signal noise than
analog cables. HDMI eliminates the digital-to-analog and analog-to-digital conversion other interfaces
require. Therefore, HDMI typically produces the best quality picture and sound compared to other types
of connections.

The HDMI ports are found either on the video card or motherboard on the back/side of the computer. It is
important to note that not all computers and video cards have HDMI connectors; old computer may
use Display Port, DVI, or VGA technology.

USB–C Display Port HDMI

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Computer System Unit 1 … 69.

Expansion slots

An expansion slot refers to any of the slots on a motherboard that can hold an expansion card to expand
the computer's functionality, like a video card, network card, or sound card. The expansion card is
plugged directly into the expansion port so that the motherboard has direct access to the hardware.
A list of expansion slots commonly found in a computer and the devices associated with those slots.
• AGP - Video card.
• AMR - Modem, sound card.
• CNR - Modem, network card, sound card.
• EISA - SCSI, network card, video card.
• ISA - Network card, sound card, video card.
• PCI - Network card, SCSI, sound card, video card.
• PCI Express - Video card, modem, sound card, network card.
• VESA - Video card.
Many of the above expansion card slots are obsolete. It is mostly going to encounter AGP, PCI, and PCI
Express when working with computers today.

Figure: 1.34 Expansion Slots

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SUMMARY

Characteristics of Computer ● Petabyte PB 1024 TB
● Exabyte EB 1024 PB
1. Speed 2. Accuracy ● Zettabyte ZB 1024 EB
3. Reliability 4. Storage ● Yottabyte YB
5. Retrieving data and programs 6. Automation ● Bronobyte BB 1024 Z
7. Versatility 8. Communications ● Geopbyte GpB/GeB 1024YB(Unofficial)
9. Diligence 10. No Feelings 1024BB (Unofficial)
11. Consistency 12. Precision
Classification of Computer

Application of Computers On the basis of size, computers are classified into following four

1. Education 2. Entertainment main groups.
3. E-Commerce 4. Health Care
5. Science and Engineering 6. Publishing 1. Microcomputer.
7. Government and E-Governance 8. Home
9. Agriculture 10. Energy 2. Minicomputer.

3. Mainframe computer.

4. Supercomputer.

Features of Mobile computing,

Evolution of Computer ● Easy to handle and carry these small devices.

1. First Era: Pre-history era or Pre-mechanical era (500BC-1642) ● Data can be transferred easily between users.
2. Second Era: Mechanical era (1642-1890)
3. Third Era: Electro-mechanical era (1890-1945) ● Collect simulated data to current zone or your time.
4. Fourth Era: Electronic era (1946-today)
Generations of Computers, ● Arbitrary network, easily connect to other environment and

a. First Generation (1946 - 1956) transmit data.
b. Second Generation (1956 - 1965)
c. Third Generation (1965 - 1973) ● Having fast processor speed.
d. Fourth Generation (1973 - 2020)
e. Fifth Generation (2020 and beyond) ● Good battery life.

Computer Speed and Measurement Unit ● Huge memory capacity.

● No time constraints

● No place constraints

● Reduced costs and time etc

Computer speed and its measurement can be taken in different Applications of Mobile computing,

ways: ● Traffic control and information ● Emergencies Situation

1. Bit Width ● Use in Business ● Credit Card Verification

2. Clock Cycles ● Replacement of Fixed Networks ● Entertainment

3. Execution Cores ● Construction ● Defense

4. CPU Speed Measurements ● Airlines industry ● Banking

5. Bandwidth ● Medical ● Rural area

6. Storage Unit ● News reporting ● Health care

In computer the information, data, software, or anything that ● Education etc

are store in memory. Their storage capacity is measured in Computer Organization,

terms of either: The Von Neumann model is characterized by five major

Unit Abbreviation Storage subsystems:

● Bit b 1or 0 1. Input

● Nibble - 4 bits 2. Arithmetic-logic unit (ALU)

● Byte B 8 bits 3. Control unit

● Kilobyte KB 1024 B 4. Memory

● Megabyte MB 1024 KB 5. Output

● Gigabyte GB 1024 MB

● Terabyte TB 1024 GB

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Computer System Unit 1 … 71.

According to Von Neuman model, a computer is organized in such of phosphor 3. No radiation emitted.
a way that it should be able to perform the following four functions;
1. Receive input information from outside world. 3. Emit radiation. 4. Not harmful for eyes.
2. Process the information
3. Produce output to communicate with the outside world, and 4. Harmful for the eyes. 5. Picture quality is low.
4. Store information for future reference
5. Picture quality is high. 6. Viewing angle is very small.

6. Viewing angle is large. 7. Cost is high.

7. Cost is low. 8. Occupy small space.

8. Occupy large space. 9. Low power consumption.

Concepts of System Buses 9. High power consumption. 10. Screen size is about to

A bus is a data communication path over which bits of information 10. Screen size is not exact of its mention size.

are transmitted between the various computer components. The given size. 11.No flicking.

expansion slot can be: 11. Screen is flicking 12. Better to keep the default

1. ISA bus 2. AGP bus 12. Resolution can be changed resolution.

3. PCI bus 4. USB according to our need 13. New technology.

5. SCSI frequently.

Memory 13. Old technology.

Memory can be basically classified into two major categories. They Computer Peripherals
are;
1. Primary Memory or Main memory, Internal memory and The different types of peripherals are;
2. Secondary memory or Auxiliary memory or External memory
Difference between CRT and LCD Monitor, ● Input devices that are used to feed data and instructions into
the computer such as keyboard, mouse, scanner,
CRT LCD microphone, digital camera, track ball, touch pad etc.

1. Uses vacuum tube and 1. Uses Liquid Crystal. ● Storage devices which are used to store data for backup like
magnetic disks such as hard disk; CD-ROMs, flash memory,
electron guns. 2. While supplying electricity, magnetic tape etc.

2. Light glow while striking crystal becomes ● Output devices that are used to get the information from the
processor or display the result to outside world; such as,
electron on a coated surface transparent. VDU, printers, plotters, speakers etc.

EXERCISE

Short Answer Questions

1. Define computer on the basis of current used.
2. Define diligence characteristics of computer.
3. What is computer era?
4. Define clock cycles.
5. Define data bandwidth.
6. Define mobile computing.
7. What do you mean by computer architecture?
8. Define register.
9. Define cache memory.
10. Define bus in computer.
11. Define ROM.
12. Define input.
13. Define output.

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.72 … Computer Science–I

14. Define magnetic memory.
15. Define optical memory.
16. Define peripherals.

Long Answer Questions

1. Define and explain the generation of computer.
2. Define and explain the electronic era.
3. Define and explain the classification of computer on the basis of size and speed.
4. Briefly explain the architecture layer of computer.
5. Draw block diagram of a computer and explain its components briefly.
6. What do you mean by CPU? Explain briefly.
7. Explain different types of bus in computer.
8. What is memory? Explain different types of memory.
9. Difference between primary and secondary memory.
10. Difference between DRAM and SRAM.
11. Difference between RAM and ROM.
12. Explain different types of ROM.
13. Briefly explain different input devices.
14. Briefly explain different output devices.
15. Explain softcopy output devices.
16. Explain hardcopy output devices.
17. Differentiate between impact and nonimpact printer.
18. Differentiate between serial and parallel port.

Write Short Notes On

1. LCD Monitor 9. Light pen 17. Modem
2. HDMI port 10. Touch screen 18. Trackball
3. Mouse 11. MICR 19. Compiler versus Interpreter
4. Monitor 12. System software 20. Laser printer
5. USB 13. OCR 21. Charles Babbage
6. Cache memory 14. Joystick 22. Touch pads and light pens
7. NIC 15. Bar Code Reader 23. Computer interface
8. Scanner 16. Control Unit 24. Versatile characteristics

■■■

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Number System

and Conversion

Boolean Logic

 LEARNING OBJECTIVES

After studying this chapter, the students will be able to understand to:

We know the definition of computer from first unit. Our computer is digital electronic device

........ means store and process data digitally. In this unit importance of number, number system their ..........
relation and switching frequently between number system, use and conversion as well as basic
..

flow of logic electronically inside the computer system in terms of Boolean, Boolean laws of

algebra and Boolean expression will have the basic knowledge at the end this unit.

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.74 … Computer Science–I

NUMBER SYSTEM

There are different types of number systems in use, some are more common and others are rarely used.
Each number system uses different types and number of symbols, digits, alphabets or some other
representation mechanism. The total number of symbols or digits in a number system is called a radix or
base. The base or radix indicates the total number of possible digits or symbols in a number system. For
example; decimal number system is known as base ten systems because it uses ten different digits from 0
to 9. Depending upon the position of a digit in a number, the value it represents also varies. The position
of an individual digit in a number is called its weight. For example; in decimal number 123, the weight of 3
is 100(=1), of 2 is 101(=10) and 1 is 102(=100).

We frequently use some kind of calculation, which may be done orally, with paper and pencil or calculator
or some other type of calculating aid. All types of calculations involve numbers. Our day to day
calculation is based on decimal digits 0 to 9 and their combinations for large values. Decimal digits are
accepted universally wherever we go. Schools and colleges, business and offices or doctors, engineers and
scientists or a common person, everybody uses decimal numbers. Therefore, decimal number system is an
essential part of our daily life and we are using since we know to count and calculate.

There are many other number systems like binary number, octal number, hexadecimal number, ternary
number etc. Though a common person may not need these numbers, persons who deal with machines
may need any or all of these numbers. Machines have their own language. Therefore, unlike man,
machines do not understand the decimal numbers. So, to deal or work with machines, we must
understand and use the language of that machine.

Computer, as a machine, uses base two number system, which uses only two digits '0' and '1', each of
which is called 'bit'. Each decimal digit of a number is converted into a series of 1's and 0's (generally a
combination of 8-bits, such as for decimal 15, binary sequence could be 00001111). Moreover, all digital
computer components and building blocks like logic gates are based on binary systems. Therefore, binary
number is the language of computer.

Similarly, since each digit of a decimal number is converted into 8-bits binary, a larger decimal number
with more than one digit will become lengthy and occupy large space in memory. Such large binary
numbers are difficult to remember and make calculations with them. Hence, some other number system,
like octal and hexadecimal number systems are used. Octal system uses base eight (from 0 to 7) and
hexadecimal system uses base sixteen (numbers from 0 to F- which is equivalent to 0 to 9 and A to F for 10
to 15). Octal number is equivalent to 3-bit binary number (such as octal number 7 for 111, and 9F for
100011111). Hence, different number systems are necessary in computing either for actual computation
within the computer or to store in memory devices or for the larger calculations

Decimal (Denary) System

Decimal number system is a base-10 system which means there are 10 distinct symbols (digits) 0 through
9. The value that the digits represent depends on the “weight” or position they hold. For example;
consider a decimal number 1024. It can be represented in position system as;

Position 4th 3rd 2nd 1st

Weights 103 102 101 100

Value 1024

4 * 100(1) = 4
2 * 101(10) = 20
0 * 102(100) = 0
1 * 103(1000) = 1000

Total = (1024)10

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Number System and Conversion Boolean Logic Unit 2 … 75.

If the number has both an integer part and fractional part then the two portions should be dealt separately.
Let’s consider a decimal number 1024.25. Here, the position system is;

Integer Part = 1 × 1000 + 0 × 100 + 2 × 10 + 4 × 1 = 1024

Fractional Part = 2 × 10-1 + 5 × 10-2 = 0.25

Binary Numbering System

Every computer stores numbers, letters and other characters in a coded form. The code uses two digits '0'
and '1'. Each digit is called 'bit'. Each and every character in storage is represented by a string of 0s and 1s.
Therefore, the numbering system uses base 2. The possible symbols being used 0 and 1. The 0s and 1s can
be arranged in various combinations to represent all the numbers, letters and symbols that can be entered
into the computer.

Computers have been designed to use binary numbers because of the following reasons:

1. Because of the use of two distinct binary bits, it simplifies the design of the circuits, reduces the cost
and improves the reliability.

2. Computer only identifies signals in the form of digital pulses, either high voltage of hot state “ON”
(1) or a low voltage of cold state “OFF” (0).

3. Everything that can be done with a base of 10 can also be done in binary.

As binary system is a base 2 system, the position weights are used on the powers of 2. For example; (1011)2
can be represented in binary as;

Position 4th 3rd 2nd 1st
Weights 23 22 21 20
Value 1011
Decimal
1 × 23 + 0 × 22 + 1 × 21 + 1 × 20 = 11

Octal Numbering System

Octal system was issued to provide a shorthand way to deal with the long string of 1s and 0s created in
binary. It is a base-8 system using the digits 0 through 7. The position and weights are based on the
powers of 8.

In the Octal numbering system, we write numbers in sequence until all digits in a specific position are
filled (exhausted). Then we initialize the given position with 0 and add 1 to the next position.

Decimal Octal

00

11

22

33

44

55

66

77

8 (7)8+ (1)8 = (10)8

9 11

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10 12

11 13

12 14

13 15

14 16

15 17

16 (17)8+ (1)8 = (20)8
So on So on

Most of the computer manufacturers are using the octal numbering system or base 8 systems. This
numbering system can be used to represent group of three binary bits from right to left as a single octal
number.

Hexadecimal Numbering System

The hexadecimal system is also used to provide a shorthand way to deal with long string of 1s and 0s
created in binary. It contains the digits 0 through 9 and the letters A through F. In hexadecimal system,
four binary digits grouped together produce a digit in the 16 or hexadecimal number system. Therefore, it
has 16 unique digits, and called as hexadecimal number system.

Decimal Hexadecimal

00

11

22

33

44

55

66

77

88

99

10 A

11 B

12 C

13 D

14 E

15 F

16 10

17 11

18 12

19 13

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Number System and Conversion Boolean Logic Unit 2 … 77.

20 14
21 15
22 16
23 17
24 18
25 19
26 1A
27 1B
28 1C
29 1D
30 1E
31 1F
32 20 likewise

Binary Calculation

Addition, subtraction, multiplication, and division of binary numbers are carried out in the same way as it
is in decimal system. Let us take operations one by one.

a. Addition : Rules for carrying out addition of binary numbers are as follows:

0+0=0

0+1=1

1+ 0 = 1

1+1= 0, with a carry over '1' to the next higher column.

Eg. For adding (110101)2 and (101111)2

Binary Decimal

110101 53

+ 101111 + 47

1100100 100

(1100100)2 is equivalent to (100)10 in decimal system
b. Subtraction : Rules for subtraction of binary numbers are as follows:

0–0=0
1–0=1
1–1=0
0 – 1 = 1, with a borrow of '1' from next higher column.
Eg. For subtracting (101111)2 from (110101)2

Binary Decimal

110101 53

+ 101111 – 47

000110 06

(110)2 is equivalent to 610 in decimal system.

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c. Multiplication : Rules for multiplication of binary numbers are as follows:
0*0=0
0*1=0
1*0=0
1*1=1
For multiplying (10110)2 with (1101)2

Eg.

Binary Decimal

10110 22

× 1101 × 13

10110 66

00000 +22

10110 286

+10110

100011110

(100011110)2 is equivalent to (286)10 in decimal system.

d. Division: Division for binary numbers can be carried out by following same rules as those applicable
to decimal system. It means, division is a series of repeated subtraction of divisor from the dividend.

Binary Decimal

For dividing (100011)2 by (101)2 35/5 = 7
101) 100011 (111

–101

0111

–101

0101

101

000

(111)2 is equivalent to 710 in decimal system.

Radix (Base) Conversion

The different types of number systems can be converted into one another by following certain procedures.
It means we can use any number system simultaneously (interchangeably). Let us study these conversions
procedures one by one.

Conversion of Decimal Number System to Other Number systems

Decimal system can be converted to other systems by using the following two methods:

a. Remainder Method: This is the most commonly used method for carrying out conversion from
decimal system to other systems. It involves the following steps:

i. Divide the given number of decimal system by the radix (base) R of the proposed system. From
this, we will get a quotient Q1 and a remainder R1.

ii. Divide the quotient Q1 by the radix R again to get quotient Q2 and a remainder R2.

iii. Divide the quotient Q2 by the radix R again to get quotient Q3 and a remainder R3.

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Number System and Conversion Boolean Logic Unit 2 … 79.

This process of division of the successive quotients by the radix R of the proposed system should be
repeated until the quotient n becomes less than radix R. Thus, the required number can be obtained
by writing the last quotient first and then remainders in the reverse order. i.e. Qn Rn Rn-1 Rn-2
……..R3 R2 R1

b. Power Method: This method involves the following steps:-

i. Subtracting the highest number which is obtained by raising the radix to the power of the
proposed system. R1 be the remainder.

ii. Subtracting the next highest number from this remainder R1.

iii. This procedure should be repeated until the remainder is zero.

iv. Write the multiplication factors in the sequential order in such a way that the powers which
have been used should be multiplied by 1 and the number with missing ones should be
multiplied by zero.

c. Fractions Part: The integer part of the fraction can be converted to other systems by following the
remainder or power method. The fraction part can be converted to other systems by using following
steps.

i. Find out the radix of the system to which fraction has to be converted.

ii. Multiply fraction with radix. Let the fraction part of this product be F and resulting integer be I.

iii. Multiply the resulting fraction part F with radix again; we will get F1 and I1.

iv. The above steps should be repeatedly done until the fraction part vanishes, or exceeds at least
4/5 decimal places.

v. The required fraction number in the required system with radix R would be I1 I2 I3……..In.

Eg.

Using Power Method

(300)10

Radix of given system = 10

Radix of given system to be changed = 2

Power of radix which are less than 300

Position 9th 8th 7th 6th 5th 4th 3rd 2nd 1st
Weights 28 27 26 25 24 23 22 21 20
Weights Value 256 128 64 32 16 8 4 2 1

The solution is obtained by raising the power of change base system and subtracted from the given
number. Raised power is 1 and remaining is 0.

300

– 256 ← 28 → 1

R 44

-32 ← 25 → 1

R1 12

-8 ← 23 → 1
R2 4

- 4 ← 22 → 1

R3 0

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.80 … Computer Science–I

28 27 26 25 24 23 22 21 20

10 0 1 0 1 1 0 0

Therefore (300)10 = (100101100)2
Using Remainder Method
(300)10 to base 2

2 300

2 150 – 0

2 75 – 0

2 37 – 1

2 18 – 1

2 9 –0

2 4 –1

2 2 –0

2 1 –0

Therefore (300)10 = (100101100)2
i. Decimal to Binary (Fraction)

Fraction Part = 0.35
Radix = 2

FI

0.35 * 2 = 0.70 0

0.70 * 2 = 0.40 1
0.40 * 2 = 0.80 0

0.80 * 2 = 0.60 1
0.60 * 2 = 0.20 1

0.20 * 2 = 0.40 0
0.40 * 2 = 0.80 0

Therefore (0.35)10 = (0.0101100…)2
ii. Decimal to Octal

Converting the decimal value to octal by using Remainder Method
Eg.
Convert (119)10 to Octal
Here,

Base is 8.

8 119

8 14 – 7

8 1 –6

0 –1

Therefore (119)10 = (167)8

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Number System and Conversion Boolean Logic Unit 2 … 81.

Octal to Decimal (Fraction)
For converting Octal Fraction to Decimal Fraction, each octal fraction digit is divided by its position
weight and sum to obtain the equivallent decimal fraction number.
For example,
Convert (0.34)8 to decimal

or
(0.34)8 = (?)10

= 3 * 8-1 + 4 * 8-2
= 3/8 + 4/64
= 0.375 + 0.6625
= 0.4375
Therefore, (0.34)8 = (0.4375)10
(Note: Similarly, fraction number of hexadecimal to decimal and fraction number of binary to
decimal can be converted.)
iii. Decimal to Hexadecimal
Converting the decimal value to hexadecimal by using Remainder Method
Eg.
Convert (7551)10 to Hexadecimal
Here,
Base is 16.

16 7551

16 471 – 15

16 29 – 7

16 1 – 13

00000 0 – 1

Therefore (7551) 10 = (1D7F) 16

Conversion of Binary Number System to Other Number Systems

i. Binary to Decimal

We can convert binary to decimal by multiplying each binary digit with its position weight and
added to obtain the equivalent decimal number.

Eg. Convert (11011010)2 to Decimal

Position 8th 7th 6th 5th 4th 3rd 2nd 1st

Weights 27 26 25 24 23 22 21 20
Given value 11011010

0 × 20 = 0
1 × 21 = 2
0 × 22 = 0
1 × 23 = 8
1 × 24 = 16

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0 × 25 = 0

1 × 26 = 64

1 × 27 = 128

(218)10

Therefore (11011010)2 = (218)10
ii. Binary to Octal

A binary number can be converted into its octal equivalent by using two methods:

Method I
For converting a binary number to its octal equivalents, we need to first convert binary number to
decimal form and then convert decimal to octal form.

Method II
We can also convert the binary to octal number by grouping three binary digits to produce a single
octal number. Grouping can be done from right to left.
Let us take example, the binary number (110011101)2 can be represented as

Given Number 1 10 01 1 1 01

Power representation 22 21 20 22 21 20 22 21 20

Octal representation 635

Therefore (110011101)2 = (635)8

iii. Binary to Hexadecimal

For converting a binary number to hexadecimal form, it should be grouped into fours bits from the
right to left.

Eg. Convert (11101100111)2 to Hexadecimal

Here,

0111 0110 0111

76 7

Therefore (011101100111)2 = (767)16

Conversion of Octal Number System to Other Number systems

i. Octal to Decimal

For converting octal to decimal, each octal digit should be multiplied by its position weight and sum
to obtain the equivalent decimal number.

Eg. Convert (454)8 to decimal

Position 3rd 2nd 1st

Weights 82 81 80

Value 454

4 × 80 = 4
5 × 81 = 40
4 × 82 = 256

300
Therefore (454)8 = (300)10

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