d by a customer to access the network. The Computer For all its complexity, the typical computer has only a small number of components, as shown in Figure 5-1. These are the central processing unit (CPU), main memory, secondary memory, input/output (I/O) devices, and a parallel bus that ties all the components together. It also has two types of software that make the computer useful to a human. The first is application software such as word processors, spreadsheet applications, presentation software, and MP3 encoders. The second is the operating system that manages the goings on within the computer including hard- ware component inventory and file location. In a sense, the operating system is the executive assistant to the computer itself; some mainframe manufacturers refer to their operating system as the EXEC. The concept of building modular computers came about in the 1940s when Hungarian-born mathematician John Von Neumann applied the work he had done in logic and game theory to the challenge of building large electronic computers (Figure 5-2). As one of the primary contribu- tors to the design of the Electronic Numerical Integrator and Computer (ENIAC), Von Neumann introduced the concept of stored program con- trol and modular computing-the design under which all modern com- puters are built today. The internals of a typical modern computer are shown in Figure 5-3. Secondary I/O Devices Figure 5-1 Memory Memory Computer components 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 Figure 5-2 A section of the original ENIAC The CPU The CPU is the brain of the computer. Its job is to receive data input from the I/O devices (keyboard, mouse, modem, etc.), manipulate the data in some way-based on a set of commands from a resident application- and package the newly gerrymandered data for presentation 