Geographic Information Systems: An Introduction, 3rd Edition

7.1 Computers

The heart of a computer consists of one or more integrated-circuit microprocessors, or central processing units (CPUs), which contain the circuitry necessary to interpret and execute program instructions for processing data and controlling peripheral equipment. Reduced instruction set computer architecture (RISC), a relatively new technological development based on high-level programming, offers a number of improvements as compared with the traditional CPU. For example, it has a wider range of basic functions and can carry out more complex operations with greater power and speed. The choice between RISC and the traditional CPU is more a matter of division of labor between the processor and a low-level operating system. Users will notice no particular difference other than the speed.

Data are stored in the working memory along with the operating system and the application program, which may be entered from secondary storage as needed. The working memory is completely solid-state electronic, and therefore access to it and retrieval from it are rapid.

Random access memory (RAM) is the most common type of working memory and is relatively expensive. Professional GIS users today normally use a PC with 128 to 164 MB of RAM. The number of operations per second is expressed in megahertz. A typical operation may be to send 8-, 16-, 32-, or 64-bit bytes through the processor, or from the processor to RAM. In 2001, PCs were available with a processor speed of 400 MHz. Performance ...