Lec 10 Computer Codes

1

CS1010 Introduction to Computing

Lecture 10

Data Representation

Data Types

• _{Numeric Data consists of only numbers 0, 1, 2, …, 9}

• _{Alphabetic Data consists of only the letters A, B, C, …,}

Z in both uppercase and lower case, and blank character.

• _{Alphanumeric Data is a string of symbols where a}

symbol may be one of the letters A, B, C, …, Z in

• _{Computers store data in digital format as a series of 1s}

and 0s (known as binary code)

– _{Each 1 and 0 is called a bit}

– _{Eight bits is called a byte}

• _{The term bit comes from “binary digit”}

• _{Bytes are used to represent one character – a letter,}

number, or punctuation mark

– _{For example, the letter H is represented in binary code as}

01001000

– _{An exclamation point (!) is 01000001}

• _{Digital data is made up of discrete numbers, with each}

bit being either a 1 or a 0 – it’s either on or off, nowhere in between

• _{Analog data is made up of a continuous wave of}

information, with varying degrees in between

• _{For example:}

– _{A digital clock changes it’s digital display} once every minute to show the time

– _{An analog clock is continually moving it’s} second, minute and hour hands to show the time

How Computers Represent Data

• _{Computer processing is performed by transistors,}

which are switches with only two possible states: on and off.

• _{All computer data is converted to a series of binary}

numbers– 1 and 0. For example, you see a sentence as a collection of letters, but the computer sees each

letter as a collection of 1s and 0s.

• _{If a transistor is assigned a value of 1, it is on. If it has}

a value of 0, it is off. A computer's transistors can be

Ten different symbols in the decimal system

• _{Data representation makes it possible to convert}

letters, sounds, and images into electrical signals.

• _{Digital electronics makes it possible for computer to}

manipulate simple “on” and “off” signals to perform complex tasks.

– _{A computer’s circuits have only two states: on and}

off

– _{A binary 1 represents “on”} – _{A binary 0 represents “off”}

• _{Unlike the decimal system (base 10), the binary number}

system (base 2) uses only two digits: 0 and 1

• _{The following table lists some}

decimal numbers and their binary equivalent:

• _{Character data is composed of letters, symbols, and}

numbers that will not be used in arithmetic operations

– _{Numeric data is used in arithmetic calculations, and is}

encoded differently

• _{ASCII (American Standard Code for Information}

Interchange) requires only 7 bits for each character

• _{Extended ASCII uses 8 bits for each character. Used in}

most personal computers

– _{See the code on the next slide}

•

EBCDIC

(Extended Binary-Coded Decimal

Interchange Code) is an alternative 8-bit used

by older IBM systems.

•

Unicode

uses 16 bits and provides codes for

65,000 characters – a bonus for representing

alphabets of multiple languages

– _{Used for foreign language support}

BCD

•

BCD stands for

B

inary

C

oded

D

ecimal.

•

It is one of the early computer codes.

•

It uses

6 bits

to represent a symbol.

•

It can represent

64

(2⁶) different characters.

EBCDIC

•

EBCDIC stands for

E

xtended

B

inary

C

oded

D

ecimal

I

nterchange

C

ode.

•

It uses

8 bits

to represent a symbol.

•

It can represent

256

(2⁸) different characters.

•

Example

ASCII

• _{ASCII stands for American Standard Code for}

Information Interchange.

• _{ASCII is of two types – ASCII-7 and ASCII-8}

• _{ASCII-7 uses 7 bits to represent a symbol and It can}

represent 128(2⁷) different characters.

• _{ASCII-8 uses 8 bits to represent a symbol and It can}

represent 256(2⁸) different characters.

•

Example

In both ASCII-7 and ASCII-8, coding scheme for

128 characters is same.

Unicode

•

It uses

16 bits

to represent a symbol.

•

It can represent

65000

(2ⁱ⁶) different

characters.

•

Represent alphabet of different multiple

•

Sounds and pictures must be

transformed

into a

format the computer can understand.

•

A computer must

digitize

colors, notes, and

instrument sounds into 1s and 0s.

•

For example

, a red dot on your screen might be

represented by 1100, a green dot by 1101.

•

A

bit

is one binary digit (b)

•

A

byte

is 8 bits (B)

•

A

nibble

is 4 bits

• _Prefixes

– _{Kilo- means a 1000} – _{Mega- means million} – _{Giga- means billion}

• _{Kilobyte (KB) is approx. 1,000 bytes (1,024)}

• _{Megabyte (MB) is approx. 1,048,576 bytes (1,024 KB)}

• _{Gigabyte (GB) is approx. 1,073,741,824 bytes (1,024 MB)}

1. A(n) _______ device works with discrete numbers, whereas a(n) _______ device works with continuous data.

2. The _______ number system represents numeric data as a series of 0s and 1s.

3. Most personal computers use the _______ code to represent character data.

4. 100 Mb is larger than 100 MB. True or false?

5. A prefix that means a million bytes is _______.

1. A(n) digital device works with discrete numbers, whereas a(n) analog device works with continuous data.

2. The binary number system represents numeric data as a series of 0s and 1s.

3. Most personal computers use the extended ASCII code to represent character data.

4. 100 Mb is larger than 100 MB. False

5. A prefix that means a million bytes is Mega .

Example

/ 230 ₌

In the lab…

1. Double click on My Computer 2. Right click on C:

Exercise – Free Space

•

Determine the

“free space”

on all drives on a

machine in the lab

Drive

Free space

Bytes GB