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Introducing Geographic Information Systems with ArcGIS: A Workbook Approach to Learning GIS, 3rd Edition by Michael D. Kennedy

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Computer Software: In General

Computers, considered at the most fundamental level, do only three things:26 get input, manipulate data, and produce output; that is, read bits, stir bits, and write bits. What tells the computer what to do? In the early days of computers, more than half a century ago, each individual instruction to a computer came from outside, one at a time. This process was soon automated so that external media, such as perforated paper tape or magnetic tape, contained the instructions. Then, several scientists27 got the idea of placing the instructions in the store of the computer itself. This major breakthrough in computer development allowed the computer to execute one group of instructions and then, on the basis of testing bits in its memory (e.g., Is number “a” larger than number “b”?), execute another group of instruction in a different place in that memory. This let the computer simulate “reasoning” and “decision making.” This concept of a stored program revolutionized computer use.

The modern computer may hold an immense number of data sets and store a large number of programs. If a given program or data set not being used usually resides in “slow” disk (usually electromechanical) memory. Dealing with large numbers of diverse elements requires a management scheme. With computers this takes the form of an operating system that allows the user to execute specific programs when desired, connects the computer to other computers (e.g., by way of the Internet ...

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