Syaran

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Submitted By syaransai
Words 14549
Pages 59
MEC/CEC, CA/CWA, B.Com & B.Sc.

Master Minds

4. Data Storage, Retrieval & DBMS
Q.No.1. Write about different coding schemes. BCD:

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BCD stands for binary Coded Decimal system. This is a 6 bit code i.e. each character is expressed in terms of a 6 bit code. There will be 64 ways of representing digits, alphabets and special symbols. There is no parity bit in this coding scheme.

ASCII: ASCII stands for American Standard Code for Information Interchange. This code is extensively used in small computers, peripherals, instruments and communication devices. It is a seven-bit code and has replaced many of the special codes that were previously used. Microcomputers using 8-bit word length use 7 bits to represent the basic code. The 8th bit is used for parity or it may be permanently 1 or 0. With 7 bits, up to 128 characters can be coded. A letter, digit or special symbol is called a character. It includes upper and lower case alphabets, numbers, punctuation marks, special and control characters. Here the first 3 bits are zone bits and the remaining 4 bits represent digit values.

ASCII-8: A newer version of ASCII is ASCII-8 code, which is an 8-bit code. With 8 bits, the code capacity is extended to 256 characters.

EBCDIC: EBCDIC stands for Extended Binary Coded Decimal Interchange Code. It is a standard character code for large computers. It is a 8-bit code without parity and 9th bit can be used as parity bit. Using 8 bits 256 characters can be coded. In ASCII-8 and EBCDIC, the first 4 bits are known as zone bits and the remaining 4 bits represent digit values.

Inf. Tech._13e_Data storage, retrieval & DBMS ____________________________4.1

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Q.No.2. Define the term key. Write about different types of keys?

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Key: A key is a set of one or more columns whose combined values