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).

One byte for   character A                             01000001

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?