In Chapter 3 you had a chance to explore some of the properties of the binary number system. You are already aware that within the computer the binary number system is the system of choice, both for all forms of data storage and for all internal processing of operations. As human beings, we normally don’t choose to do our work in binary form. Our communications are made up of language, images, and sounds. For written communications, and for our own data storage, we most frequently use alphanumeric characters and symbols, representing English or some other language.
At some point, original data, whether character, image, sound, or some other form, must be brought initially into the computer and converted into an appropriate computer representation so that it can be processed, stored, and used within the computer system. The fundamental process is shown in Figure 4.1. Different input devices are used for this purpose. The particular choice of input device reflects the original form of the data, and also the desired data representation within the computer.
ALPHANUMERIC CHARACTER DATA
Much of the data that will be used in a computer are originally provided in human-readable form, specifically in the form of letters of the alphabet, numbers, and punctuation, whether English or some other language. The text of a word processing document, the numbers that we use as input to a calculation, the names and addresses in a database, the transaction data that constitutes a credit card purchase, the keywords, variable names, and formulas that make up a computer program, all are examples of data input that is made up of letters, numbers, and punctuation.
The volume of multimedia data, particularly video, but also sound and even high resolution still images, often makes it impossible or impractical to store, transmit, and manipulate the data in its normal form. Instead it is desirable or, in some cases, necessary to compress the data. This is particularly true for video clips, real-time streaming video with sound, lengthy sound clips, and images that are to be transmitted across the Internet through modem connections.
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Data from a keyboard enters the computer in the form of a character stream, which includes nonprinting characters as well as printing characters. Image scanning with optical character recognition, voice input, and various special devices, such as bar code readers, can also be used to create alphanumeric data.
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