Number Systems | Computer Science - Representing Characters in Memory | 11th Computer Science : Chapter 2 : Number Systems

Chapter: 11th Computer Science : Chapter 2 : Number Systems

Representing Characters in Memory

As represented in introduction, all the input data given to the computer should be in understandable format.

Representing Characters in Memory

As represented in introduction, all the input data given to the computer should be in understandable format. In general, 26 uppercase letters, 26 lowercase letters, 0 to 9 digits and special characters are used in a computer, which is called character set. All these character set are denoted through numbers only. All Characters in the character set needs a common encoding system. There are several encoding systems used for computer. They are

• BCD – Binary Coded Decimal

• EBCDIC – Extended Binary Coded Decimal Interchange Code

• ASCII – American Standard Code for Information Interchange

• Unicode

• ISCII - Indian Standard Code for Information Interchange

1. Binary Coded Decimal (BCD)

This encoding system is not in the practice right now. This is 2⁶ bit encoding system. This can handle 2⁶ = 64 characters only.

2. American Standard Code for Information Interchange (ASCII)

This is the most popular encoding system recognized by United States. Most of the computers use this system. Remember this encoding system can handle English characters only. This can handle 2⁷ bit which means 128 characters.

In this system, each character has individual number (Refer Appendix).

The new edition (version) ASCII -8, has 2⁸ bits and can handle 256 characters are represented from 0 to 255 unique numbers.

The ASCII code equivalent to the uppercase letter ‘A’ is 65. The binary representation of ASCII (7 bit) value is 1000001. Also 01000001 in ASCII-8 bit.

3. Extended Binary Coded Decimal Interchange Code (EBCDIC)

This is similar to ASCII Code with 8 bit representation. This coding system is formulated by International Business Machine(IBM). The coding system can handle 256 characters. The input code in ASCII can be converted to EBCDIC system and vice - versa.

4. Indian Standard Code for Information Interchange (ISCII)

ISCII is the system of handling the character of Indian local languages. This as a 8-bit coding system. Therefore it can handle 256 (2⁸) characters. This system is formulated by the department of Electronics in India in the year 1986-88 and recognized by Bureau of Indian Standards (BIS). Now this coding system is integrated with Unicode.

5. Unicode

This coding system is used in most of the modern computers. The popular coding scheme after ASCII is Unicode. ASCII can represent only 256 characters. Therefore English and European Languages alone can be handled by ASCII. Particularly there was a situation, when the languages like Tamil, Malayalam, Kannada and Telugu could not be represented by ASCII. Hence, the Unicode was generated to handle all the coding system of Universal languages. This is 16 bit code and can handle 65536 characters.

Unicode scheme is denoted by hexadecimal numbers. The Unicode table of Tamil, Malayalam, Telugu and Kannada is shown Table 2.6

Appendix

American Standard Code for Information Interchange (ASCII)

(Few specific characters only)

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