INTRODUCTION

A block diagram of the basic computer organization is shown in figure. In this figure, the solid lines indicate the flow of instruction and data and the dotted lines represent the control exercised by the control unit. It displays the five major building blocks (functional units) of a digital computer system. These five units correspond to the five basic operations, performed by all computer systems. The functions of each of these units are described below.

A computer system can be useful, only when it is able to communicate with its external environment (its users). As shown in Figure 3.1, the input-output devices (abbreviated I/O devices) provide the means of communication between the computer and the outer world. They are also known as peripheral devices, because they surround the CPU and the memory of a computer system. Input devices are used to enter data form the outside world into primary storage, and output devices supply the results of processing from the primary storage to the users. A wide variety of I/O devices are now available. For a particular application, one type may be more desirable than another. There are some devices, which are used for both input and output functions. The goal of this chapter is to familiarize you with the various types of I/O devices available for computer systems.

In the discussion above, we saw that the CPU contains the necessary circuitry for data processing and controlling the other components of a system. However, one thing it does not have built into it is the place to store programs and data, which are needed during data processing. We also saw that the CPU does contain several registers for storing data and instructions, but these are very small areas, which can hold only a few bytes at a time, and are just sufficient to hold only one or two instructions and the corresponding data. If the instructions and data of a program being executed by the CPU, were to reside in secondary storage like a disk, and fetched and loaded one by one into the registers of the CPU as the program execution proceeded, this would lead to the CPU being idle most of the time, because there is a large speed mismatch between the rate at which CPU can process data and the rate at which data can be transferred from disk to CPU registers. For example, a CPU can process data at a rate of about five nanosecond/byte, and a disk reader can read data at a speed of around five microsecond/byte.

NUMBER SYSTEMS

COMPUTER CODES

The lowest-level programming language (except for computers that utilize programmable microcode) Machine languages are the only languages understood by computers. While easily understood by computers, machine languages are almost impossible for humans to use because they consist entirely of numbers. Programmers, therefore, use either a high-level programming language or an assembly language. An assembly language contains the same instructions as a machine language, but the instructions and variables have names instead of being just numbers.

There are many aspects to be considered in the study of compilers. Usually the study encompasses more that just the strict definition of a compiler. According to Webopedia, a compiler is:

A programming language is an artificial language designed to express computations that can be performed by a machine, particularly a computer. Programming languages can be used to create programs that control the behavior of a machine, to express algorithms precisely, or as a mode of human communication.

We saw above that planning a program involves defining its logic (the correct sequence of instructions needed to solve the problem at hand). The term algorithm is often used to refer to the logic of a program. It is a step-by-step description of how to arrive at the solution of the given problem. It may be formally defined as a sequence of instructions, designed in a manner that, if the instructions are executed in the specified sequence, the desired results will be obtained. In order to qualify as an algorithm