001 . What is a Computer ?

a computer is a device capable of performing computations and making  logical decisions at speeds millions, and even billions, of time faster than human beings can. For example ,many of today's personal computers can perform hundreds of millions additions per second. a person operating a desk calculator might require decades to complete the same number of calculations a powerful personal computer can perform in one second. [points to ponder: how would you know whether the person added the numbers correctly ?] today's fastest supercomputers can perform hundreds of billions of additions per second-about as many calculations as hundreds of thousands of people could perform in one year! and trillion instruction -per- second computers are already functioning in research laboratories!

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

The various device[such as the keyboard,screen,disks, memory and processing units] that comprise a computer system are referred to as hardware. The computer programs that run on a computer are referred to as software. hardware cost have been declining dramatically in recent years, to the point that personal computers have become a commodity. unfortunately, software development cost have been rising steadily as programmers develop ever more powerful and complex applications, without being able to significantly improve the technology of software development. In this book you will learn proven software development methods that can reduce software development costs- top down stepwise refinement, fictionalization and object- oriented programming. object- oriented programming is widely believed to be the significant breakthroughs that can greatly enhance programmer productivity.