to a human user at another I/O device (monitor). The CPU has its own set of sub- components. These include a clock, an arithmetic-logic unit (ALU), and Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Premises Technologies Chapter 5 Figure 5-3 I/O Cards PC internals Power Supply showing major components Hard Drive and CD Drives Parallel Bus registers. The clock is the device that provides synchronization and tim- ing to all devices in the computer, and is characterized by the number of clock cycles per second it is capable of generating. These cycles are called Hertz; modern systems today operate at a range of speeds as high as 4 Megahertz, or MHz. The faster the clock, the faster the machine can perform computing operations. The ALU is the specialized silicon intelligence in the CPU that per- forms the mathematical permutations that make the CPU useful. All functions performed by a computer-word processing, spreadsheets, multimedia, videoconferencing all functions-are viewed by the com- puter as mathematical functions and, therefore, are executed as such. It is the job of the ALU to carry out these mathematical permutations. Registers are nothing more than very fast memory located close to the ALU for rapid input/output functions during execution cycles. Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Premises Technologies Premises Technologies Main Memory Main memory, sometimes called random access memory (RAM), is another measure of the "goodness" of a computer today. RAM is the seg- ment of memory in a computer used for execution space and as a place to store operating system, data, and application files that are in current use. RAM is silicon-based, solid-state memor