Information Representation
Codes - Representing Character Sets

Coding systems are employed by computers in order to represent various characters, numbers, and control keys that the computer user selects on the keyboard. Three of the more popular coding systems are:

  1. ASCII (American Standard Code for Information Interchange)
  2. EBCDIC (Extended Binary Coded Decimal Interchange Code)
  3. BCD (Binary Coded Decimal)

They differ in how many digits or bits they use to represent a character. Below are some examples:

ASCII
7 bit		 EBCDIC
8 bit		 BCD
4 bit
1000001 = A
1000010 = B
1000011 = C
1000100 = D
1000101 = E
etc.		 11000001 = A
11000010 = B
11000011 = C
11000100 = D
11000101 = E
etc.		 0000 = 0
0001 = 1
0010 = 2
0011 = 3
0100 = 4
etc.

In each system the character or number is represented by a sequence of binary digits which can only have values of 0 or 1. The ASCII system uses seven 0 or 1 digits or bits to represent the letters of the alphabet, while EBCDIC uses eight bits. BCD uses four bits to represent the numbers 0 to 9.