CPU - Central Processing Unit

CPU (pronounced as separate letters) is the abbreviation forcentral processing unit.

Sometimes referred to simply as the central processor, but more commonly called processor, the CPU is the brains of the computer where most calculations take place. In terms of computing power, the CPU is the most important element of a computer system.

Microprocessor

A silicon chip that contains a CPU. In the world of personal computers, the terms microprocessor and CPU are used interchangeably. At the heart of all personal computers and most workstations sits a microprocessor. Microprocessors also control the logic of almost all digital devices, from clock radios to fuel-injection systemsfor automobiles.

Three basic characteristics differentiate microprocessors:

Instruction set: The set of instructions that the microprocessor can execute.

bandwidth : The number of bits processed in a single instruction.

clock speed : Given in megahertz (MHz), the clock speed determines how many instructions per second the processor can execute.

In both cases, the higher the value, the more powerful the CPU. For example, a 32-bit microprocessor that runsat 50MHz is more powerful than a 16-bit microprocessor that runs at 25MHz.

In addition to bandwidth and clock speed, microprocessors are classified as being either RISC (reduced instruction set computer) or CISC(complex instruction set computer).

See the Microprocessor Comparison Chart page in the Quick Referencesection of Webopedia for a comparison of microprocessors.

OS - operating system

The operating system is the most important program that runs on acomputer. Every general-purpose computer must have an operating system to run other programs. Operating systems perform basic tasks, such as recognizing input from the keyboard, sending output to the display screen, keeping track of files and directories on the disk, and controlling peripheral devices such as disk drives andprinters.

For large systems, the operating system has even greater responsibilities and powers. It is like a traffic cop -- it makes sure that different programs and users running at the same time do not interfere with each other. The operating system is also responsible for security, ensuring that unauthorized users do not access the system.

Classification of Operating systems

Multi-user: Allows two or more users to run programs at the same time. Some operating systems permit hundreds or even thousands of concurrent users.

Multiprocessing : Supports running a program on more than one CPU.

Multitasking : Allows more than one program to run concurrently.

Multithreading : Allows different parts of a single program to run concurrently.

Real time: Responds to input instantly. General-purpose operating systems, such as DOS and UNIX, are not real-time.

Operating systems provide a software platform on top of which other programs, called application programs, can run. The application programs must be written to run on top of a particular operating system. Your choice of operating system, therefore, determines to a great extent the applications you can run. For PCs, the most popular operating systems are DOS, OS/2, and Windows, but others are available, such as Linux.

As a user, you normally interact with the operating system through a set of commands. For example, the DOS operating system contains commands such as COPY and RENAME for copying files and changing the names of files, respectively. The commands are accepted and executed by a part of the operating system called thecommand processor or command line interpreter. Graphical user interfaces allow you to enter commands by pointing and clicking at objects that appear on the screen.

Chip

A small piece of semiconducting material (usually silicon) on which an integrated circuit is embedded. A typical chip is less than a few square inches and can contain millions of electronic components (transistors). Computers consist of many chips placed on electronic boards called printed circuit boards.

There are different types of chips. For example, CPU chips (also called microprocessors) contain an entire processing unit, whereas memory chips contain blank memory.

Chips come in a variety of packages. The three most common are:

DIPs :Dual in-line packages are the traditional buglike chips that have anywhere from 8 to 40 legs, evenly divided in two rows.

PGAs : Pin-grid arrays are square chips in which the pinsare arranged in concentric squares.

SIPs : Single in-line packages are chips that have just one row of legs in a straight line like a comb.

In addition to these types of chips, there are also single in-line memory modules(SIMMs), which consist of up to nine chips packaged as a single unit.

Integrated circuit

Another name for a chip, an integrated circuit (IC) is a small electronic device made out of a semiconductor material. The first integrated circuit was developed in the 1950s by Jack Kilby of Texas Instrumentsand Robert Noyce of Fairchild Semiconductor.

Integrated circuits are used for a variety of devices, including microprocessors, audio and video equipment, and automobiles. Integrated circuits are often classified by the number of transistors and other electronic components they contain:

SSI (small-scale integration):Up to 100 electronic components per chip

MSI (medium-scale integration):From 100 to 3,000 electronic components per chip

LSI (large-scale integration):From 3,000 to 100,000 electronic components per chip

VLSI (very large-scale integration):From 100,000 to 1,000,000 electronic components per chip

ULSI (ultra large-scale integration): More than 1 million electronic components per chip

High-level language

A programming language such as C, FORTRAN, or Pascal that enables a programmer to write programs that are more or less independent of a particular type of computer. Such languages are considered high-level because they are closer to human languages and further from machine languages. In contrast, assembly languagesare considered low-level because they are very close to machine languages.

The main advantage of high-level languages over low-level languages is that they are easier to read, write, and maintain. Ultimately, programs written in a high-level language must be translated into machine language by acompiler or interpreter.

The first high-level programming languages were designed in the 1950s. Now there are dozens of different languages, including Ada, Algol, BASIC, COBOL, C, C++, FORTRAN, LISP, Pascal, and Prolog.

Assembly language

All of the files that comprise an application, including the resource, security management, versioning, sharing and deployment information. An assembly may appear as a single DLL or EXE file, or as multiple files, and is roughly the equivalent of a COM module.

Transistor

A device composed of semiconductor material that amplifies a signal or opens or closes a circuit. Invented in 1947 at Bell Labs, transistors have become the key ingredient of all digital circuits, including computers. Today's microprocessors contains tens of millions of microscopic transistors.

Prior to the invention of transistors, digital circuits were composed of vacuum tubes, which had many disadvantages. They were much larger, required more energy, dissipated more heat, and were more prone to failures. It's safe to say that without the invention of transistors, computing as we know it today would not be possible.

Vacuum Tube

1. 
   In electronics, vacuum tube, electron tube (in North America), tube, or valve (in British English) is a device that controls electric current through a vacuum in a sealed container. Vacuum tubes mostly rely on thermionic emission of electrons from a hot filament or a cathode heated by the filament.

Machine language

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.

Programs written in high-level languages are translated into assembly language or machine language by acompiler. Assembly language programs are translated into machine language by a program called anassembler.

Every CPU has its own unique machine language. Programs must be rewritten or recompiled, therefore, to runon different types of computers.

Magnetic drum

A direct-access, or random-access, storage device. A magnetic drum, also referred to as drum, is a metal cylinder coated with magnetic iron-oxide material on which data and programs can be stored. Magnetic drums were once used as a primary storage device but have since been implemented as auxiliary storage devices.

The tracks on a magnetic drum are assigned to channels located around the circumference of the drum, forming adjacent circular bands that wind around the drum. A single drum can have up to 200 tracks. As the drum rotates at a speed of up to 3,000 rpm, the device's read/write heads deposit magnetized spots on the drum during the write operation and sense these spots during a read operation. This action is similar to that of a magnetic tape ordisk drive.

Unlike some disk packs, the magnetic drum cannot be physically removed. The drum is permanently mounted in the device. Magnetic drums are able to retrieve data at a quicker rate than tape or disk devices but are not able to store as much data as either of them.

Fifth Generation of Computer (1989-present)

Scientists are working hard on the 5^th generation computers with quite a few breakthroughs. It is based on the technique of Artificial Intelligence (AI). Computers can understand spoken words & imitate human reasoning. Can respond to its surroundings  using different types of sensors. Scientists are constantly working to increase the processing power of computers.

 They are trying to create a computer with real IQ with the help of advanced programming and technologies. IBM Watson computers one example that outsmarts Harvard University Students. The advancement in modern technologies will revolutionize the computer in future

  Advantages

• ULSI technology
• Development of true artificial intelligence
• Development of Natural language processing
• Advancement in Parallel Processing
• Advancement in Superconductor technology
• More user friendly interfaces with multimedia features
• Availability of very powerful and compact computers at cheaper rates

Fourth Generation of Computer (1975-1989)

The fourth generation computers started with the invention of Microprocessor. The Microprocessor contains thousands of ICs. Hoff Ted produced the first microprocessor in 1971 for Intel. It was known as Intel 4004. The technology of integrated circuits improved rapidly. The LSI (Large Scale Integration) circuit and VLSI (Very Large Scale Integration) circuit was designed. It greatly reduced the size of computer. The size of modern Microprocessors is usually one square inch. It can contain millions of electronic circuits. The examples of fourth generation computers are Apple Macintosh & IBM PC.

Advantages

• More powerful and reliable than previous generations.
• Small in size
• Fast processing power with less power consumption
• Fan for heat discharging and thus to keep cold.
• No air conditioning required.
• Totally general purpose
• Commercial production
• Less need of repair.
• Cheapest among all generations
• All types of High level languages can be used in this type of computers.

Disadvantages

·         The latest technology is required for manufacturing of Microprocessors.

Third Generation of Computer (1964-1975)

The Third generation computers used the integrated circuits (IC). Jack Kilby developed the concept of integrated circuit in 1958. It was an important invention in the computer field. The first IC was invented and used in 1961. The size of an IC is about ¼ square inch. A single IC chip may contain thousands of transistors. The computer became smaller in size, faster, more reliable and less expensive. The examples of third generation computers are IBM 370, IBM System/360, UNIVAC 1108 and UNIVAC AC 9000 etc.

Advantages

• Smaller in size as compared to previous generations.
• More reliable.
• Used less energy
• Produced less heat as compared to the previous two generations of computers.
• Better speed and could calculate data in nanoseconds.
• Used fan for heat discharge to prevent damage.
• Maintenance cost was low because hardware failure is rare.
• Totally general purpose
• Could be used for high-level languages.
• Good storage
• Versatile to an extent
• Less expensive
• Better accuracy
• Commercial production increased.
• Used mouse and keyboard for input.

Disadvantages

• Air conditioning was required.
• Highly sophisticated technology required for the manufacturing of IC chips. 

Second Generation of Computer (1955-1964)

 The second generation computers used Transistors. The scientists at Bell laboratories developed transistor in 1947. These scientists include John Barden, William Brattain and William Shockley. The size of the computers was decreased by replacing vacuum tubes with transistors.   

The examples of second generation computers are IBM 7094 series, IBM 1400 series and CDC 164 etc.

Advantages

·         Smaller in size as compared to the first generation computers.

·         The 2nd generation Computers were more reliable

·         Used less energy and were not heated.

·         Wider commercial use

·         Better portability as compared to the first generation computers.

·         Better speed and could calculate data in microseconds

·         Used faster peripherals like tape drives, magnetic disks, printer etc.

·         Used Assembly language instead of Machine language.

·         Accuracy improved.

Disadvantages

·         Cooling system was required

·         Constant maintenance was required

·         Commercial production was difficult

·         Only used for specific purposes

·         Costly and not versatile

·         Puch cards were used for input.

First Generation of Computer (1942-1955)

The beginning of commercial computer is from UNIVAC. It was developed by two scientist Mauchly and Echert at the Census Department of United States in 1947. The first generation computers were used during 1942-1955. They were based on Vacuum Tubes.
Examples of first generation computers are ENIVAC and UNIVAC-1

Advantages

• Vacuum tubes were the only electronic component available during those days.
• Vacuum tube technology made possible to make electronic digital computers.
• These computers could calculate data in millisecond.

Disadvantages

·         The computers were very large in size.

·         They consumed a large amount of energy.

·         They heated very soon due to thousands of vacuum tubes.

·         They were not very reliable.

·         Air conditioning was required.

·         Constant maintenance was required.

·         Non-portable.

·         Costly commercial production.

·         Limited commercial use.

·         Very slow speed.

·         Limited programming capabilities.

·          Used machine language only.

·           Used punch cards for input.

·           Not versatile and very faulty.

·           Used magnetic drums which provide very less data storage. 

Computer Generations

The development of electronic computer can be divided into five generations depending upon the technologies used. Following are the five generations of computer.