1.3 Information Coding Scheme

Topic 1.3

Computer System

1.3 Information Coding Scheme

1

Learning Outcome

a) Describe how computer encode
characters using ASCII (8 bits), EBCDIC and
Unicode.

c) Differentiate the coding system based on
number of bits and total number of
character represented

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Data Representation-Recap

• How computers represent data? 3
Data & instructions can be represented electronically by
using two unique binary digits 1 (on) and 0 (off) and bytes
which are 8 bits combined together to represent a character
up to 256 characters.
• Data representation refers to the form in which data is

stored, processed, and transmitted in computers.
• Digital data is text, numbers, graphics, sound, and video

that has been converted into bit patterns of 0s and 1s
called binary numbers.

Representing Numbers

Computers Number Binary
represent all Representation
numeric data 0
(numbers) with the 1 00000000
binary system. 2 00000001
3 00000010
4 00000011 4
5 00000100
… 00000101
254
255 …
11111110
11111111

Representing Text
(Character Set)

How can a Answer:
computer Information
represents non- Coding Scheme
numeric
characters 5
(character data )?

(such as what you are

reading now)

Information Coding
Scheme /System

What is The combinations of 0s
Information and 1s that represent
uppercase and lowercase
Coding letters, numbers, &
Scheme?
special symbols.

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Information Coding
Scheme /System

Why are Computers rely on logic circuits,
Information which are controlled by electronic
switches whose state can be either
Coding
Schemes on or off.
necessary?
Each switch’s on/off state is
represented by one bit, whose 7

value is either 0 or 1.

Coding schemes translate real
world data into a form that
computers can process easily.

Information Coding
Scheme

 ASCII
[American Standard Code for Information
Interchange]

 EBCDIC
[Extended Binary Coded Decimal Interchange Code]

 Unicode 8
[Uniform code capable of representing all world’s
languages]

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This figure shows how a letter is converted to binary form and back.

Information Coding Scheme :

ASCII

• ASCII (pronounced “ask-ee”) is the most widely used coding
scheme to represent a set of characters.

Number of bits • Uses 8 bits to represent a character.
Number of • Represents 256 characters (28 = 256).
characters
Usage • Primarily used on minicomputers, personal
computers and servers.
Advantage
• ASCII coding scheme uses 8 bits to represent a
character, meaning that storing data in ASCII takes
up less memory.

Disadvantage • The 256 characters that are represented by ASCII
coding scheme are only sufficient for English and
Westerns European languages but is not large 10
enough for Asian and other languages that use
different alphabets.

Example of *Encoding in ASCII

P a y space $ 8 !

01010000 01100001 01111001 00100000 00100100 00111000 00100001

*Encoding means converting data into a digital form

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Information Coding Scheme : EBCDIC

• EBCDIC is widely considered to be an outdated coding
system, but is still used in some equipment, mainly on IBM
mainframe and IBM midrange computer operating systems
in order to allow for continued use of software written many
years ago that expects an EBCDIC communication
environment.

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Information Coding Scheme :
EBCDIC

Number of bits • Uses 8 bits to represent a character.
Number of • Represents 256 characters (28 = 256).
characters
Usage • Primarily used on IBM mainframe, midrange
systems and high-end servers.
Advantage
• EBCDIC coding scheme uses 8 bits to represent a
character, meaning that storing data in EBCDIC
takes up less memory.

Disadvantage • The 256 characters that are represented by EBCDIC
coding scheme are only sufficient for English and
Westerns European languages but is not large
enough for Asian and other languages that use 13
different alphabets.

Example of *Encoding in EBCDIC

PAY space $ 8 !

11010111 11000001 11101000 00100000 01011011 11111000 01011010

*Encoding means converting data into a digital form

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Information Coding Scheme : Unicode

• Unicode is a 16 bit coding scheme that has the capacity of
representing all the world’s current languages as well as classic
and historical languages, in 65, 536 characters and symbols.

Number of bits • Uses 16 bits to represent a character.
Number of • Represents 65,536 characters (216 = 65, 536).
characters
Usage • Implemented in several operating systems
including Windows, Mac OS, and Linux.
Advantage
• Unicode can represent 65,536 characters, (216 =
Disadvantage 65,536) capable of representing almost all the
world’s current languages, classical and historical
languages and symbols.

• Unicode coding scheme uses 16 bits to represent a 15
character, meaning that storing data in Unicode
takes up more memory.

Example of *Encoding in Unicode

P A Y space $ 8 !

0000 0000 0000 0000 0000 0000 0000
0000 0000 0000 0000 0000 0000 0000
0101 0100 0101 0010 0010 0011 0010
0000 0001 1001 0000 0100 1000 0001

*Encoding means converting data into a digital form

Information Coding Scheme : Unicode

Examples of Asian languages and historical 17
symbols that can be represented using Unicode

coding scheme.

Information Coding Scheme : Unicode

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Part of Unicode Chart

Part of ASCII , EBCDIC and
Unicode Binary Codes

Character Information Coding Scheme

ASCII EBCDIC Unicode

A 01000001 11000001 0000000001000001

B 01000010 11000010 0000000001000010

E 01000101 110000101 0000000001000101

The figure shows the combination of bits (0s and 1s) is 19
unique for each character in the ASCII ,EBCDIC and Unicode

Coding Scheme.

Summary :Information Coding
Scheme

Characteristic ASCII EBCDIC Unicode

Number of bits Uses 8 bits to Uses 8 bits to Uses 16 bits to
represent a represent a represent a
character character character

Number of Represents 256 Represents 256 Represents
characters characters characters 65,536 characters
represented (28 = 256) (28 = 256) (216 = 65,536)

Usage Primarily used on Primarily used on Implemented in
minicomputers, IBM mainframe, several OS
personal midrange systems (Windows, Mac
computers and and high-end OS X, Linux)
server servers
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Differences between
Information Coding Scheme

Characteristic ASCII EBCDIC Unicode

Number of bits Uses 8 bits to Uses 8 bits to Uses 16 bits to
represent a represent a represent a
character character character

Number of Represents 256 Represents 256 Represents
characters
represented characters characters 65,536

(28 = 256) (28 = 256) characters

(216 = 65,536)

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Learning Outcome

b) Calculate the total number of bits/bytes in
given word based on each coding scheme.

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Summary :Information Coding
Scheme

Characteristic ASCII EBCDIC Unicode

Number of bits Uses 8 bits to Uses 8 bits to Uses 16 bits to
represent a represent a represent a
character character character

Number of Represents 256 Represents 256 Represents
characters characters characters 65,536 characters
represented (28 = 256) (28 = 256) (216 = 65,536)

Usage Primarily used on Primarily used on Implemented in
minicomputers, IBM mainframe, several OS
personal midrange systems (Windows, Mac
computers and and high-end OS X, Linux)
server servers
23

Differences between
Information Coding Scheme

Characteristic ASCII EBCDIC Unicode

Number of bits Uses 8 bits to Uses 8 bits to Uses 16 bits to
represent a represent a represent a
character character character

Number of Represents 256 Represents 256 Represents
characters
represented characters characters 65,536

(28 = 256) (28 = 256) characters

(216 = 65,536)

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Number of bits/bytes used by Information
Coding Scheme to represent phrases

HELLO WORLD!

HEL LO WO R L D !

1 2 3 4 5 6 7 8 9 10 11 12

ASCII ECBDIC UNICODE

Bits 12 characters x 8 bits 12 characters x 8 bits 12 characters x 16 bits

= 96 bits = 96 bits = 192 bits

Bytes 96 bits /8 96 bits /8 192 bits /8
* = 12 bytes = 12 bytes = 24 bytes

25

*8 bits grouped together as a unit, they form a byte.

Number of bits used by Information
Coding Scheme to represent phrase

“ S E L AMA T DA T ANG K E KMS ” . .

12 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

ASCII ECBDIC UNICODE

Bits 25 characters x 8 bits 25 characters x 8 bits 25 characters x 16 bits

= 200 bits = 200 bits = 400 bits

Bytes 200 bits /8 200 bits /8 400 bits /8
* = 25 bytes = 25 bytes = 50 bytes

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*8 bits grouped together as a unit, they form a byte.

‘A’ Number of bits used by Information
Coding Scheme to represent phrase

f o r C omp u t e r S c i e n c e !

ASCII ECBDIC UNICODE

Bits

Bytes 27
*

*8 bits grouped together as a unit, they form a byte.

Conclusion

• When discussing numbers and alphabetical characters,
it is important to remember that all data being
transmitted through a computer system is represented
by bits or circuit notation.

• A fingerprint, picture, or company logo is also converted
by appropriate programs into patterns of binary digits.

Now that you understand bits, bytes, and how
computers represent data, it is important to
understand their relationship to the rest of the system.

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Chapter Concept :
Topic 1.3 Information Coding Scheme

1. How computer presents data?

2. Define Coding System/Scheme.

3. List three coding systems.

4. Explain ASCII from the number of bits, number of characters it

represents and the usage.

5. Explain EBCDIC from the number of bits, number of characters it

represents and the usage.

6. State the type of computer that still uses EBCDIC.

7. Explain Unicode from the number of bits, number of characters it

represents and the usage.

8. Discuss the advantage of using Unicode.

9. Discuss the advantage of using ASCII.

10. Explain why Unicode is becoming popular compared to ASCII and

EBCDIC. 29
11. Differentiate between ASCII, EBCDIC and Unicode from the

number of bits and number of characters.

Discussion

1. How many bits would it take to represent the following
phrase using the ASCII code?
Introduction to Computer Science.

2. Give the benefit of using ASCII.
3. Give the benefit of using Unicode over ASCII.
4. How many different characters can Unicode represent?
5. How many different characters can ASCII represent?
6. You are designing a computer system for use

worldwide, which character encoding scheme should
you use and why?

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