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 trillions of additions per second!

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, hard disk, memory, DVDs 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. In this book, you will learn proven methods that are reducing software development costsobject-oriented programming and (in our optional Software Engineering Case Study in Chapters 27, 9 and 13) object-oriented design.