# Data Representation in Computer

## How Computers Represent Data

All symbols, pictures or words must be reduced to a string of binary digits.
A binary digit is called a bit and represents either a 0 or a 1.
These are the only digits in the binary or base 2, number system used by computers.
A string of eight bits used to store one number or character in a computer system is called a byte (see Figure 0.2).

#### The computer representation in ASCII for the name Alice is

• 01000001                             A
• 01001100                             L
• 01001001                             I
• 01000011                             C
• 01000101                             E
To represent the numbers 0 through 9 and the letters a through z and A through Z, computer designers have created coding systems consisting of several hundred standard codes.
In one code, for instance, the binary number 01000001 stands for the letter A.
Two common coding systems are Extended Binary Coded Decimal Interchange Code (EBCDIC) and American Standard Code for Information Interchange (ASCII).
EBCDIC represents every number, alphabetic character, or special character with eight bits, used primarily in IBM and other mainframe computers.
ASCII was originally designed as a seven-bit code, but most computers use eight-bit versions.
ASCII is used in data transmission, PCs and some larger computers.
The computers store a picture by creating a grid overlay of the picture.
Each single point in this grid, or matrix is called a pixel (picture element) and consists of a number of bits.
Data Representation
How is a letter converted to binary form and back?