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Mạng và viễn thông P4

Data and the Binary Code System ‘Data’, a plural noun, the term used to describe information which is storedand processed by is in computers. It is essential to know how such data are represented electronically before we can begin to understand how it can be communicated between computers, communication devices (e.g. facsimile machines) other data storage or devices. As a necessary introduction to the concept of ‘digital’ transmission, this chapter is devoted to a description of tha method of representing textual and numeric information which is called the ‘binary code’. . | Networks and Telecommunications Design and Operation Second Edition. Martin P. Clark Copyright 1991 1997 John Wiley Sons Ltd ISBNs 0-471-97346-7 Hardback 0-470-84158-3 Electronic 4 Data and the Binary Code System Data a plural noun is the term used to describe information which is stored in and processed by computers. It is essential to know how such data are represented electronically before we can begin to understand how it can be communicated between computers communication devices e.g. facsimile machines or other data storage devices. As a necessary introduction to the concept of digital transmission this chapter is devoted to a description of tha method of representing textual and numeric information which is called the binary code . 4.1 THE BINARY CODE Binary code is a means of representing numbers. Normally numbers are quoted in decimal or ten-state code. A single digit in decimal code may represent any of ten different unit values from nought to nine and is written as one of the figures 0 1 2 3 4 5 6 7 8 9. Numbers greater than nine are represented by two or more digits twenty for example is represented by two digits 20 the first 2 indicating the number of tens so that twice ten must be added to 0 units making twenty in all. In a three digit decimal number such as 235 the first digit indicates the number of hundreds or ten tens the second digit the number of tens and the third digit the number of units . The principle extends to numbers of greater value comprising four or indeed many more digits. Consider now another means of representing numbers using only a two-state or binary code system. In such a system a single digit is restricted to one of two values either zero or one. How then are values of two or more to be represented The answer as in the decimal case is to use more digits. Two itself is represented as the two digits one-zero or 10. In the binary code scheme therefore 10 does not mean ten but two . The rationale for this is similar to the .