Chapter03 - Chapter3 DataRepresentation DataandComputers...

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Chapter 3 Data Representation
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    2 Data and Computers Computers are multimedia devices, dealing with many categories of information. Computers store, present, and help modify: Numbers Text Audio Images and graphics Video
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    3 Analog and Digital Information Computers are finite. Computer memory and other hardware devices have only so much room to store and manipulate a certain amount of data. The goal of data representation is to represent enough of the world to satisfy our computational needs and our senses of sight and sound.
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    4 Analog and Digital Information Information can be represented in one of two ways: analog or digital . Analog data: A continuous representation, analogous to the actual information it represents. Digital data: A series of discrete representations, breaking the information up into separate elements.
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    5 Analog and Digital Information A mercury thermometer exemplifies analog data as it continually rises and falls in direct proportion to the temperature. Digital displays only show discrete information.
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    6 Analog and Digital Information Computers cannot work well with analog information, so we digitize it by sampling it at discrete intervals and representing each interval by a numeric value.
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    7 Electronic Signals An analog signal continually fluctuates up and down in voltage. But a digital signal has only a high or low state, corresponding to the two binary digits. An analog and a digital signal
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    8 Electronic Signals All electronic signals (both analog and digital) degrade as they move down a line. That is, the voltage of the signal fluctuates due to environmental effects. Degradation of analog and digital signals
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    9 Electronic Signals  (Cont’d) Even when it has deteriorated, it is possible to distinguish the 2 states of a digital signal by comparison to the threshold. Periodically, a digital signal can be reclocked to regain its original shape. No such process is available for analog signals.
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    10 Representing Text
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    11 Representing Text To represent a text document in digital form, we need to be able to represent every possible character that may appear. There is a finite number of characters to represent, so the general approach is to list them all and assign each a binary string.
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    12 Representing Text A character set is a list of characters and the codes used to represent each one. In 1960, a survey revealed 60 different characters sets in use. At IBM alone there were 9 different sets. By agreeing to use ONE particular character set, computer manufacturers have made the processing of text data easier.
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    13 The ASCII Character Set ASCII stands for A merican S tandard C ode for I nformation I nterchange. The
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This note was uploaded on 12/15/2010 for the course CSE CSE 1520 taught by Professor Paul during the Spring '09 term at York University.

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Chapter03 - Chapter3 DataRepresentation DataandComputers...

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