1.3 Information Coding Scheme_2122

Computer system

1.3 Information Coding Scheme

SC015-COMPUTER SCIENCE

Chapter 1: Computer System

1.3 Information Coding Scheme

Learning Outcomes :
At the end of the lesson, students should be
able to:

a) Describe how computers encode characters using ASCII (8 bits),
EBCDIC, Unicode.
b) Calculate the total number of bits/bytes in a given word based on each
coding scheme. (clo1)

c) Differentiate the coding system based on number of bits and total
number of character represented. (clo3)

1.3 Information Coding Scheme

What is Information Coding Scheme?

Definition :

The combinations of 0s and 1s that represent characters
are defined by patterns.

Example:
Hey = 01001000 01100101 01111001

1.3 Information Coding Scheme

Type of coding systems
:

1.3 Information Coding Scheme

Example of coding system
:

1.3 Information Coding Scheme

ASCII

 ASCII = American Standard Code for Information

Interchange.

 ASCII uses 8 bits to represent a character.

 The 8th bit in the ASCII code is a parity bit.

 This is used to perform a parity check (used for error checking).

 For example, the ASCII code for lower case z is 122 and is shown
below:

Parity 64 32 16 8 4 2 1
Bit

01111010

1.3 Information Coding Scheme

ASCII

 There are two (2) ways for error checking:

 Even parity: Where the 8th bit is set such that the total number of 1s
in the 8-bit code word is even.

01000001

 Odd Parity: The 8th bit is set such that the total number of 1s in the 8-
bit code word is odd.

11000001

1.3 Information Coding Scheme

ASCII

• Most widely used to represent data.
• Sufficient for English and Western European character only

• Traditionally used with PCs.
• ASCII uses 8 bits to represent 1 character.

• ASCII provides codes for 256 characters
(28=256).

1.3 Information Coding Scheme

ASCII

Characters include:
• number :(e.g. 4,7,8)
• letter – uppercase and lowercase:(Y, y)
• punctuation mark (?, !), or other

• symbol (^, &)

• that is represented by a single byte in the
ASCII and EBCDIC coding scheme.

1.3 Information Coding Scheme

1.3 Information Coding Scheme ASCII

• Example :

COMPUTER

1 2 3 4 5 6 78

ASCII

8 characters involved in the word
8 bits per character
8 characters X 8 bits = 64 bits used in the

memory of the computer

64Byte= bits / 8 = 8 bytes

1.3 Information Coding Scheme ASCII

• Example :

C O M P U T E R.

1 2 3 4 5 6 7 89

ASCII

9 characters involved in the word
8 bits per character
9 characters X 8 bits = 73 bits used in the

memory of the computer

73Byte= bits / 8 = 9 bytes

1.3 Information Coding Scheme

• Example : ASCII

COMPUTER SCIENCE

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

16 characters including space

ASCII

16 characters involved in the word
8 bits per character
16 characters X 8 bits = 128 bits used in the

memory of the computer

Byte= 128 bits / 8 = 16 bytes

1.3 Information Coding Scheme

EBCDIC

• The Extended Binary Coded Decimal Interchange
Code (EBCDIC) uses 8 bits (4 bits for zone, 4 bits for
digit) to represent a symbol in the data.

00000000

Zone Digits

EBCDIC allows 2 8 = 256 combinations of bits.

1.3 Information Coding Scheme

EBCDIC

• Extended Binary-Coded Decimal Interchange Code
• Developed by IBM

• Sufficient for English and Western European
• Primarily used on mainframes and high-end servers

• Uses 8 digit code (8 bits) for 1 character
• Can represent up to 256 characters - (28 = 256)

1.3 Information Coding Scheme

EBCDIC CODE

1.3 Information Coding Scheme EBCDIC

• Example :

COMPUTER

1 2 3 4 5 6 78

EBCDIC

8 characters involved in the word
8 bits per character
8 characters X 8 bits = 64 bits used in the

memory of the computer

64Byte= bits / 8 = 8 bytes

1.3 Information Coding Scheme EBCDIC

• Example :

C O M P U T E R.

1 2 3 4 5 6 7 89

EBCDIC

9 characters involved in the word
8 bits per character
9 characters X 8 bits = 73 bits used in the

memory of the computer

73Byte= bits / 8 = 9 bytes

1.3 Information Coding Scheme

• Example : EBCDIC

COMPUTER SCIENCE

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

16 characters including space

EBCDIC

16 characters involved in the word
8 bits per character
16 characters X 8 bits = 128 bits used in the

memory of the computer

Byte= 128 bits / 8 = 16 bytes

1.3 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.

1.3 Information Coding Scheme

Unicode

• Unicode is a universal character encoding standard
for the representation of text which includes letters,
numbers and symbols in multi-lingual environments.

• Unicode codes can uniquely represent any
character or symbol present in any language
like Chinese, Japanese etc.

1.3 Information Coding Scheme

Unicode

• Can represent 65,536 characters and
symbols(216)

• Uses 16 digit code (16 bits) for 1 character.

• Implemented in several OS (Windows, Mac
OS & Linux).

1.3 Information Coding Scheme Unicode

Scan for more
Unicode
example

Click for more Unicode example

1.3 Information Coding Scheme

Unicode

Why uses Unicode is the most widely used coding
scheme?

ASCII and EBCDIC are limited to just the basic English
letters and common symbols.
Today computers use many different symbols
including letters from languages that don’t use
English letters (e.g. Hebrew, Chinese, etc) and
international symbols (e.g. the English pound sign).

Advantage
Can be used worldwide with consistent and
unambiguous results.
Modern programs are moving towards using Unicode
to store letters and symbols.

1.3 Information Coding Scheme Unicode

• Example :

COMPUTER

1 2 3 4 5 6 78

EBCDIC

8 characters involved in the word
16 bits per character
8 characters X 16 bits = 128 bits used in the

memory of the computer

Byte= 128 bits / 8 = 16 bytes

1.3 Information Coding Scheme Unicode

• Example :

C O M P U T E R.

1 2 3 4 5 6 7 89

EBCDIC

9 characters involved in the word
16 bits per character
9 characters X 16 bits = 144 bits used in the

memory of the computer

Byte= 144 bits / 8 = 18 bytes

1.3 Information Coding Scheme

• Example : Unicode

COMPUTER SCIENCE

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

16 characters including space

EBCDIC

16 characters involved in the word
16 bits per character
16 characters X 16 bits = 256 bits used in the

memory of the computer

Byte= 256 bits / 8 = 32 bytes

1.3 Information Coding Scheme

Number of characters represented

ASCII EBCDIC Unicode

Represents Represents Represents
256 256 65,536

characters characters characters.

1.3 Information Coding Scheme

Number of bits used by a character.

ASCII EBCDIC Unicode

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

1.3 Information Coding Scheme

Context of use.

ASCII EBCDIC Unicode

used on particularly used on
many used on IBM many
different mainframe different
computer computer
system system

1.3 Information Coding Scheme

Represent different number of bits/bytes
used for each character..

ASCII 8 bits 1 byte

EBCDIC 8 bits 1 byte

Unicode 16 bits 2 bytes

1.3 Information Coding Scheme

ASCII 0 100000 1
Letter “A” = 1 byte

01000001

EBCDIC

Letter “A” = 1 byte

Unicode
0000000001000001

Letter “A” = 2 bytes

1.3 Information Coding Scheme

Represent different language.

ASCII EBCDIC Unicode

English & English & World’s current
Western Western languages,
languages languages classic &
historical
languages

1.3 Information Coding Scheme

Differences between ASCII, EBCDIC and Unicode.

Criteria ASCII EBCDIC Unicode

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

Number of Can represent 256 Can represent 256 Can represent
characters characters (28 = 256) characters (28 = 256) more than 65,536
represent characters and

Context of use symbols

used on many particularly used on used on many
different IBM different computer

computer system mainframe system

1.3 Information Coding Scheme

Q1. How many bits would it take to represent

the following phrase using ASCII code?

#I_Love Malaysia …

1.3 Information Coding Scheme

Q2. How many bits would it take to represent

the following phrase using EBCDIC code?

KMPP!!KMPP!! KMPP !

1.3 Information Coding Scheme

Q3. How many byte would it take to

represent the following phrase using Unicode
code?

KMPP is Awesome !!!

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