Computer and Communication

Computer and Communication

A computer is defined as an automatic electronic apparatus for making calculations or controlling operations that are expressible in numerical or logical terms.

Input/Output Unit
A computer uses input devices for data entry purposes. Some input devices allow direct communication between the user and the computer. While others require data to be recorded on an input medium such as a magnetisable material. Devices connected directly to a computer are said to be on-line devices; mouse, light pen, touch screen etc, are all on-line devices.

Similar to input devices, output devices have an interface between the user and the computer. These devices take machine coded outputs results from the processor and convert them into a form that can be used by human beings. In personal computers, display screens and printers are the commonly used output devices. Larger and faster printers, magnetic tapes and large disk units often accept the outputs of larger systems.

CPU
Central processing unit is the heart of any computer system. It consists of primary memory unit, arithmetic and logic unit and control unit.

Control Unit (CU)
Control unit controls all the hardware operations, ie, those of input output units, storage and of the processor itself. It fetches the requisite instructions from main storage, stores it in a number of special registers, interprets the instructions and follows the instructions to be executed by giving signals to the appropriate hardware devices.

Arithmetic and Logic Unit (ALU)
The arithmetic and logic units in computers are capable of performing addition, subtraction, division and multiplication as well as some logical operations. The control units tell the arithmetic and logic unit which operation to perform and then ensure that the necessary inputs are supplied. The arithmetic element can be compared to the calculating machines.

An arithmetic and logic unit is a digital circuit that performs a set of mathematical micro-operations of set of logic micro-operations. The ALU has a number of selection lines to select a particular micro-operation in the unit.

Memory
The memory or storage section of the computer consists of the devices used to store the information that would be used during the computations. The memory section of the computer is also used to hold both intermediate and final results as the computer proceeds through the program. Memory devices are constructed so that it is possible for the control unit to obtain any information in the memory. The time required to obtain information may vary somewhat and is determined by the type of devices used to store the information. Common storage devices are integrated circuit memories, magnetic tapes and magnetic disks.

Further the memory unit is an essential component in any digital computer since it is needed for storing the programs that are executed by the CPU. The memory unit-that communicates directly with the CPU is called the main memory and devices that provide backup storage are called auxiliary memory device. Only programs and data currently used by the processor reside in the main memory.

Memory can be divided into two categories – Primary Memory and Secondary Memory. Generally we can classify main Memory in two ways.
• RAM (Random Access Memory); and
• ROM (Read Only Memory).

Generations of Computers
First Generation of Computers
Eckert and Mauchly developed the first electronic computer ENIAC (Electronic Numerical Integrator and Calculator) in 1946 in the USA. It used high-speed vacuum tubes as switching devices and has a very small memory. The ENIAC took about 200 microseconds to add two digits and about 2400 microseconds to multiply. In 1946, Professor, John V Neumann proposed te concept of stored programming ie, the storage of machine instructions in the memory of the computer along with the data. Using this principles, Professor Marvrive Wilkes developed a computer in 1949 known as EDSAC (Electronic Delay Storage Automatic Calculator).

It used mercury delay lines for storage. The first commercial production of stored electronic computer was UNIVAC (UNIVersal Automatic Computer). During the period, computer programming was mainly done in the machine language. Assembly language was introduced during the early fifties.

Second Generation of Computers
Second generation of computers emerged around 1959 with the usage of transistors instead of vacuum tubes. Transistors made of germanium semiconductor material were highly reliable as compared to tubes since they had no filament to burn. Thus switching circuits for computers made with transistors were about 10 times more reliable, 10 times faster despite one tenth powers, occupied about one-tenth space and were 10 times cheaper when compared with computers incorporating vacuum tubes. Another major breakthrough during this period was the invention of magnetic core for storage. They were used to construct large random access memories. Magnetic disk storage was also developed during this period. The higher reliability of computers and large memory availability led to the development of high level languages like FORTRAN, COBOL, ALGOL, SNOBOL etc. good batch processing operating systems emerged during the second generation. Commercial applications like Payroll, Inventory Control, Production planning and General Ledger System were developed.


Third Generation of Computers
The third generation of computers began in 1965 with germanium transistors being replaced silicon transistors. The control circuits comprised small-scale integrated circuits, consisting of transistors, resistors and capacitors, grown on a single chip of silicon, eliminating wired interconnections between components. Thus, a desired circuits could be fabricated on a tiny piece of silicon rather than assembling several discrete components into the same circuit. Hundreds or even thousands of transistors could be connected with process of metallization to form logic circuits on the same chip.

In this generation, size of main memory reached about 100 megabytes. The combined effects of high memory, powerful CPU and large disk memories led to the development of Time Shared Operating Systems, Other high level languages were developed during this period during this period like FORTRAN IV, COBOL-68, PL/1 etc. Many important on-line systems like airline reservation, dynamic production control, interactive query and integrated data base management systems emerged on the global software scenario.

Fourth Generation of Computers
The fourth generation (1971 – 1985) of computers emerged with the Large Scale Integrated Circuits (LSIc) and Very Large Scale Integrated circuits (VLSIs) which packed about50,000 transistors in a single chip. The advent of microprocessors led to two distinct advancements in computer development. One advancement was the development was the development of personal computers through which costs came down rapidly. Floppy disks served as a low cost, high capacity backup peripherals.

The other advancement of development was the decentralization of computer organization. Individual microprocessor controlled the terminals and peripheral devices which allowed the CPU to concentrate on processing activities. Disk memory became very large. A significant development in software was the development of the most ambitious language ADA. Another development was in the field of interactive graphics.

Future Generation of Computer
Computer scientists and engineers are now talking about developing fifth generation computes that can think. The emphasis is now shifting from developing reliable, faster and smaller but dumb machines to more intelligent machines. An effective fifth-generation computer would be highly complex and intelligent electronic device conceived with the idea of intelligence (called Artificial Intelligence or AI) without going through the various stages of technical development.

Although the semiconductor memory technologies were developed, yet the VLSI technology is still evolving and more powerful microprocessors and more storage space are being added into a single chip. The contemporary computers are characterized as fourth generation computers. Some researchers classify them as the fifth generation computers. The boundary between fourth generation and fifth generation is still very blurred therefore; many researchers still believe that we are in the fourth generation.


Computers are classified by the type of data that they are designed to process. Therefore, we have the following types of computers:
• Analog Computers
• Digital Computers
• Hybrid Computers

Analog Computers
A device, which operates on a data in the form of continuously variable physical quantities, is called an analog computer. Data, which are obtained through measurement, are called continuous data. Analog computing systems are frequently used to control processes such as those found in an oil refinery where flow measurements and temperature measurements are important.

Digital Computer
A device, which manipulates discrete data and performs arithmetic and logic operations on these data, is known as a digital computer. Date, which are obtained by counting, are called discrete data. All computers used for business and scientific applications are digital computers.

Hybrid Computer
This device used desirable features of both analog and digital computers.