What Is a Computer?

A computer is a device capable of performing computations and making logical decisions at speeds millions (even billions) of times faster than human beings can. For example, many of today's personal computers can perform a billion additions per second. A person operating a desk calculator could spend an entire lifetime performing calculations and still not complete as many calculations as a powerful personal computer can perform in one second. (Points to ponder: How would you know whether the person added the numbers correctly? How would you know whether the computer added the numbers correctly?) Today's fastest supercomputers can perform hundreds of billions of additions per second. And trillion-instructions-per-second computers are already functioning in research laboratories.

Computers process data under the control of sets of instructions called computer programs. These programs guide the computer through orderly sets of actions specified by people called computer programmers.

A computer consists of various devices referred to as hardware (e.g., the keyboard, screen, mouse, disks, memory, DVD, CD-ROM and processing units). The programs that run on a computer are referred to as software. Hardware costs have been declining dramatically in recent years, to the point that personal computers have become a commodity. Unfortunately, in the absence of significantly improved technology for software development, costs have been rising steadily as programmers develop ever more powerful and complex applications. In this book, you will learn proven methodologies that can reduce software development costsobject-oriented programming and (in our optional Software Engineering Case Study in Chapters 28 and 10) object-oriented design.