Generations of Computers The basic components of an

Generations of Computers The basic components of an electronic computer are electronic switches. Computers can be classified into generations based on the technology used for these switches. The older electro mechanical computers used relays, but the first electronic computers (first generation, 1944– 58) used vacuum tubes. A vacuum tube is an evacuated tube of glass that can be used as an electronic switch. Today we don’t see vacuum tubes very often except as the picture tube of televisions and computer monitors.

The second generation of computers (1959– 63) began with the development of the transistor. A transistor is a solid state device that functions as an electronic switch. Because transistors are small and can last indefinitely, this meant that second generation computers were much smaller and more reliable than first generation computers.

second generation of computers

The development of the integrated circuit brought about the third generation of computers (1964– 70). Essentially, an integrated circuit is a solid-state device on which an entire circuit—transistors and the connections between them can be created (etched). This meant that a single integrated circuit chip, not much bigger than early transistors, could replace entire circuit boards containing many transistors, again reducing the size of computers.

From here, the evolution of computing technology has been an ever increasing miniaturization of the electronic circuitry. The fourth generation (1974– ) is typically considered to be VLSI (very large-scale integration). Currently, it is possible to place many millions of transistors and the accompanying circuitry on a single integrated circuit chip. The modern era of computers had arrived.

By the mid ’ 70 s, it was possible to put the complete circuitry for the processor of a simple computer on a single chip (called a microprocessor), and the microcomputer was born. In 1977, a small garage based company called Apple Computer marketed the first commercial personal computer (PC)—the Apple II. In 1981, IBM released its version of a PC, expecting to sell a few thousand worldwide. They didn’t want to have the hassle of maintaining an operating system, so they sold the code to Bill Gates (a small time software developer), and Microsoft was born. In 1984, Apple released the “computer for the rest of us, ” the Macintosh, designed to be so easy to use that it could be used by people without special training. Based on the research done at Xerox’s Palo Alto Research Center, the Macintosh was the first commercial computer to use a mouse and a graphical user interface (GUI).

Commonly Operating Machine Particularly Used for Trade, Education & Research A computer is a machine that manipulates data according to a list of instructions. Computer can access & process data millions of times faster than humans can. A computer can store data & information in its memory, process them & produce the desired results. Computer can do a lot of different tasks such as playing games, railway reservation etc.

Computer Hardware There a great variety of different kinds of computers used for different purposes. Typically, we divide computers into categories based on their power (that is, how fast they can do computations), physical size, and cost. Four categories are usually described: § Microcomputers - Smallest, single user. Examples: workstations, desktops (PCs), notebooks, and pocket PCs § Minicomputers Refrigerator sized, handle 20– 50 users, business use § Mainframes - Larger, room sized, used by big businesses such as airlines and banks § Supercomputers - Large, very complex, used in research for large amounts of computation, such as in weather forecasting

An IBM z. Series 800 (foreground, left).

Supercomputers

LIMITATIONS OF A COMPUTER • Lack of decision making power: Computer can’t decide on their own. They do not possess this power which is a great assert of human brings. • IQ Zero: Computers are dumb machines with zero IQ. They need to be told each & every step, however minute it may be.

A computing system consists of user(s), software, procedures, hardware, and data that work together to produce an outcome. The user is the individual that uses the system to produce a result such as a written report or calculation. Typically, this is not someone trained in computer science, but s/he most likely is trained in computer use.

The software refers to the computer programs (algorithms expressed in a computer language) that allow the computer to be applied to a particular task. The procedures are the steps that the user must follow to use the software. This is usually described in the documentation (either a printed book or online documentation that is read on the computer). The hardware is the physical computer itself. Finally, the data are the facts, figures, ideas, and so on that the program will process to produce the desired information.

In this book our focus is on software, that is, with programming. However, we need to have a general understanding of the hardware of a computer to be able to write software.

Hardware components Control Unit Input devices Arithmetic/ logic Unit CPU Output devices Main memory Auxiliary storage Regardless of the size, power, or category, however, all computers work in essentially the same way and are made up of the same general components: central processing unit, main memory, input devices, output devices, and auxiliary storage.

The heart (or brains) of the computer is the central processing unit (CPU). The CPU contains the circuitry that allows the computer to do the calculations and follow the instructions of the program. The CPU is divided into two main parts: the control unit and the arithmetic/logic unit. The control unit (CU) controls the components of the computer and follows the instructions of the program. The arithmetic/logic unit (ALU) performs the computer’s arithmetic functions (such as addition) and logical functions (such as comparison of numbers). A microprocessor has the entire CPU on a single chip.

The main memory (or RAM—random access memory) is the place where the computer remembers things. The data being processed, the results or information produced, and the program instructions themselves must be present in memory while they are being used. When power to the computer is lost, the contents of memory cannot be relied upon. We therefore say that main memory is volatile. This means that main memory can only be used for short term storage.

When you think about it, it's amazing how many different types of electronic memory you encounter in daily life. Many of them have become an integral part of our vocabulary: RAM, ROM, Cache, Dynamic RAM, Static RAM, Flash memory, Virtual memory, BIOS. . . RAM is considered "random access" because you can access any memory cell directly if you know the row and column that intersect at that cell. The opposite of RAM is serial access memory (SAM). SAM stores data as a series of memory cells that can only be accessed sequentially. If the data is not in the current location, each memory cell is checked until the needed data is found. SAM works very well for memory buffers, where the data is normally stored in the order in which it will be used (a good example is the texture buffer memory on a video card). If you have been shopping for a computer, then you have heard the word "cache. " Modern computer s have both L 1 and L 2 caches, and many now also have L 3 cache. You may also have gotten advice on the topic from well meaning friends, perhaps something like "Don't buy that Celeron chip, it doesn't have any cache in it!"

Input devices are the components that the computer uses to access data that is present outside the computer system. Input devices convert the data coming from the real world into a form that the computer can process. Examples of input devices are keyboards, scanners, swipe card readers, and sensors. Output devices are the components that present results from the computer to the outside environment. They convert the computer representation to the real world representation. Examples of output devices include monitors, printers, plotters, and speakers. Since it is necessary to store programs and data for long periods of time and main memory is volatile, we need some form of longterm (nonvolatile) memory. These are the auxiliary storage devices. They include floppy disk, hard disk, CD-ROM, DVD, and tape units.

Although not traditionally considered one of the basic hardware components, communications devices are common on most computer systems today. Computer systems must be able to communicate with other computers to exchange information. Communications devices unite computers into networks (including the Internet). This is the way that applications such as web browsing and electronic mail are provided. A common communications device on a microcomputer is a cable or digital modem, which allows cable television or telephone lines to be used for computer communication.