ASCII and EBCDIC
In addition to the computations with numbers, it is also necessary to compute with characters, i.e., alphanumeric data like Letters of the alphabet (both upper-scripts and lower-scripts), symbol (like +, ×, %, −, /, etc.), numerals, etc. For example, in the database of students of a college, the name of the students, roll numbers, marks obtained in different examinations, etc., are stored in the computer.
So it is necessary to store alphanumeric data in a digital computer, or in other words it is necessary to represent the characters in binary code. Therefore several standard codes have been developed to represent characters. Among these two codes have been used extensively.
These two are 7-bit code ASCII (American Standard Code for Information Interchange) and 8-bit code EBCDIC (Extended Binary-Coded Decimal Interchange Code). However 7-bit ASCII code is more often used is digital computers and data communication purpose.
The American Standard Code for Information Interchange in short called ASCII (pronounced as Ask-ee) is widely used in digital computers and for data communication purpose. As this code is consisting of 7 bits, therefore it can represent 27 or 128 numbers of different characters. This 7-bit code for symbols and control functions is made up of a 3-bit group followed by a 4-bit group as shown in FIG 15-4.
TABLE 15-9 shows the different characters with these 4-bit and 4-bit group representation.
The other important alphanumeric code is Extended Binary-Coded Decimal Interchange Code in short EBCDIC (Pronounced as Eb-si-dik). This is an 8-bit code, so it can represent 28 or 256 codes. It is also very closely related to punch card code and used in large computer system.