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Text CodesData Processing: Text CodesA computer accepts data and instructions in machine language (0's and 1's form). My data must be represented internally by the bits 0 and 1. The binary coding schemes are used to represent data internally in the computer memory. In binary coding, every symbol of text data is represented by a group of bits. The group of bits used to represent a symbol is called a byte. Modern computers use 8 bits to represents a symbol. The most popular text code systems are:
BCD and EBCDIC BCD The BCD stands for Binary Coded Decimal. The BCD code system is one of the early code systems. It was defined by IBM for its early computer. It was one of the first code systems to represents data in binary form. This code system consisted of 6- bit code to represent a single character and maximum 64 (26) characters can be represented inside the computer. EBCDIC In BCD, 6-bit code only 64 characters can be represented. Hence, the I3CD code was extended from a 6-bit code to 8-bit code and new code system is named as EBCDIC. EBCDIC stands for Extended Binary Coded Decimal Interchange Code. In this code system, it is possible to represent 256 (2) different characters. EBCDIC code system is still used in IBM mainframe and midrange system, but it is rarely used in personal computers. ASCII ASCII stands for American Standard Code for Information and Interchange. ft is the standard code to represent alphanumeric data. It is defined by ANSI (American Standards Institute).. The first ASCII code was 7-bit code. Then ASCII 7-bit code system was extended to 8-bit code. Today, ASCII 8-bit code system is mostly used in all types of computers. This code system is popular in data communicating. Unicode Unicode is a worldwide character code standard. In this code system 16-bits (2 bytes) are used to represent a single character or symbol. Using this code system, 65, 536 (216) different characters can be represented inside the computer. The first 256 codes in Unicode are identical to the 256 codes used by ASCII system. The Unicode standard was developed in 1991 by a joint engineering team from Apple Computer Corporation and Xerox Corporation. Unicode system is supported by the popular operating systems such as Windows 2000 and OS/2 and also supported by some applications. A table is given below that shows the coding scheme of ASCII 7-bit and 8-bit EBCDIC code systems.
It is clear from the above table that each character has its unique code, The Is and Os are arranged according to the certain character code. Bit, Byte and Word Bit Bit is abbreviations of Binary Digit. It represents binary digit 0 or 1. It is defined as the smallest basic unit of storage in the computer memory that has value 0 or 1 is called bit. Byte Word The storage capacity of computer memory is measured in bytes. A group of 8- expressed as I byte. One character takes one byte space in memory. Word A group of bits representing data or instruction that form the basic information unit of the computer is called word. A word may have the length of 8-bits, 16-bits, 32-bits or more. Thus, a word of 16-bits size is called as 2-byte word.
Representations of Signed Numbers The data is represented inside the computer as a sequence of 0’s and l’s. The left most bit is generally selected for a sign bit. It is selected ‘0’ for positive number and ‘1’ for negative number. In a sign number, the left most bit represents the sign and remaining bits represent the magnitude. For example, if the basic unit is byte, the decimal numbers +41 and —41 represented in binary form as (00101001)2 and (10101001)2 respectively. must be noted that the left most bit represents the sign bit while remaining 7 represent the magnitude. Representation of Floating Point Numbers Usually, the scientific calculations involve very large or very small numbers. The floating-point number is expressed as a combination of mantissa and exponent. It is written in the following manner. M x BE Where: "M" Represents the mantissa (or magnitude) "B" Represents the base of number system. "13" Represents the exponent. For example, the number .000162 is written as 0.162 x io3. The floating- point representation is also referred to as Scientific Representation. In the memory only the mantissa and the exponents are stored. The base value is not stored. Floating point representation is very simple method to represent very large and very small numbers. It also increases the range of numbers that can be stored in a given memory size. See Also or Related Articles:
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