Computer can help you automate various
tasks that you cannot do manually. Computer can help you organize your data and
information. Computer have much more
computing and calculating.Power then an ordinary
human. Computer may help your work to be a lot easier. Computer can help you communicate with friends,
coworkers and other contacts. Computer have many search engines to help you find
information quickly.
If you use a desktop computer, you might already know that there isn't any single part called the "computer." A computer is really a system of many parts working together. The physical parts, which you can see and touch, are collectively called hardware. (Software, on the other hand, refers to the instructions, or programs, that tell the hardware what to do.)
The following illustration shows the most common hardware in a desktop computer system. Your system might look a little different, but it probably has most of these parts. A laptop computer has similar parts but combines them into a single, notebook-sized package.
Desktop computer system
Let's take a look at each of these parts.
System unit
The system unit is the core of a computer system. Usually it's a rectangular box placed on or underneath your desk. Inside this box are many electronic components that process information. The most important of these components is the central processing unit (CPU), or microprocessor, which acts as the "brain" of your computer. Another component is random access memory (RAM), which temporarily stores information that the CPU uses while the computer is on. The information stored in RAM is erased when the computer is turned off.
Almost every other part of your computer connects to the system unit using cables. The cables plug into specific ports(openings), typically on the back of the system unit. Hardware that is not part of the system unit is sometimes called aperipheral device or device.
Storage
Your computer has one or more disk drives—devices that store information on a metal or plastic disk. The disk preserves the information even when your computer is turned off.
Hard disk drive
Your computer's hard disk drive stores information on a hard disk—a rigid platter or stack of platters with a magnetic surface. Because hard disks can hold massive amounts of information, they usually serve as your computer's primary means of storage, holding almost all of your programs and files. The hard disk drive is normally located inside the system unit.
Hard disk drive
CD and DVD drives
Nearly all computers today come equipped with a CD or DVD drive, usually located on the front of the system unit. CD drives use lasers to read (retrieve) data from a CD; many CD drives can also write (record) data onto CDs. If you have a recordable disk drive, you can store copies of your files on blank CDs. You can also use a CD drive to play music CDs on your computer.
CD
DVD drives can do everything that CD drives can, plus read DVDs. If you have a DVD drive, you can watch movies on your computer. Many DVD drives can record data onto blank DVDs.
Tip
If you have a recordable CD or DVD drive, periodically back up (copy) your important files to CDs or DVDs. That way, if your hard disk ever fails, you won't lose your data.
Floppy disk drive
Floppy disk drives store information on floppy disks, also called floppies or diskettes. Compared to CDs and DVDs, floppy disks can store only a small amount of data. They also retrieve information more slowly and are more prone to damage. For these reasons, floppy disk drives are less popular than they used to be, although some computers still include them.
Floppy disk
Why are these disks called "floppy" disks? The outside is made of hard plastic, but that's just the sleeve. The disk inside is made of a thin, flexible vinyl material.
Mouse
A mouse is a small device used to point to and select items on your computer screen. Although mice come in many shapes, the typical mouse does look a bit like an actual mouse. It's small, oblong, and connected to the system unit by a long wire that resembles a tail. Some newer mice are wireless.
Mouse
A mouse usually has two buttons: A primary button (usually the left button) and a secondary button. Many mice also have a wheel between the two buttons, which allows you to scroll smoothly through screens of information.
Mouse pointers
When you move the mouse with your hand, a pointer on your screen moves in the same direction. (The pointer's appearance might change depending on where it's positioned on your screen.) When you want to select an item, you point to the item and then click (press and release) the primary button. Pointing and clicking with your mouse is the main way to interact with your computer. For more information, see Using your mouse.
Keyboard
A keyboard is used mainly for typing text into your computer. Like the keyboard on a typewriter, it has keys for letters and numbers, but it also has special keys:
The function keys, found on the top row, perform different functions depending on where they are used.
The numeric keypad, located on the right side of most keyboards, allows you to enter numbers quickly.
The navigation keys, such as the arrow keys, allow you to move your position within a document or webpage.
Keyboard
You can also use your keyboard to perform many of the same tasks you can perform with a mouse. For more information, seeUsing your keyboard.
Monitor
A monitor displays information in visual form, using text and graphics. The portion of the monitor that displays the information is called the screen. Like a television screen, a computer screen can show still or moving pictures.
There are two basic types of monitors: CRT (cathode ray tube) monitors and the newer LCD (liquid crystal display) monitors. Both types produce sharp images, but LCD monitors have the advantage of being much thinner and lighter.
LCD monitor (left); CRT monitor (right)
Printer
A printer transfers data from a computer onto paper. You don't need a printer to use your computer, but having one allows you to print e‑mail, cards, invitations, announcements, and other material. Many people also like being able to print their own photos at home.
The two main types of printers are inkjet printers and laser printers. Inkjet printers are the most popular printers for the home. They can print in black and white or in full color and can produce high-quality photographs when used with special paper. Laser printers are faster and generally better able to handle heavy use.
Inkjet printer (left); laser printer (right)
Speakers
Speakers are used to play sound. They can be built into the system unit or connected with cables. Speakers allow you to listen to music and hear sound effects from your computer.
Computer speakers
Modem
To connect your computer to the Internet, you need a modem. A modem is a device that sends and receives computer information over a telephone line or high-speed cable. Modems are sometimes built into the system unit, but higher-speed modems are usually separate components.
The first electronic computer was designed and built at the University of Pennsylvania based on vacuum tube technology. Vacuum tubes were used to perform logic operations and to store data. Generations of computers has been divided into five according to the development of technologies used to fabricate the processors, memories and I/O units.
I Generation : 1945 – 55 II Generation : 1955 – 65 III Generation : 1965 – 75 IV Generation : 1975 – 89 V Generation : 1989 to present
First Generation (ENIAC - Electronic Numerical Integrator And Calculator EDSAC – Electronic Delay Storage Automatic Calculator EDVAC – Electronic Discrete Variable Automatic Computer UNIVAC – Universal Automatic Computer IBM 701) ƒ Vacuum tubes were used – basic arithmetic operations took few milliseconds ƒ Bulky ƒ Consume more power with limited performance ƒ High cost ƒ Uses assembly language – to prepare programs. These were translated into machine level language for execution. ƒ Mercury delay line memories and Electrostatic memories were used ƒ Fixed point arithmetic was used ƒ 100 to 1000 fold increase in speed relative to the earlier mechanical and relay based electromechanical technology ƒ Punched cards and paper tape were invented to feed programs and data and to get results. ƒ Magnetic tape / magnetic drum were used as secondary memory ƒ Mainly used for scientific computations.
Second Generation (Manufacturers – IBM 7030, Digital Data Corporation’s PDP 1/5/8 Honeywell 400) ƒ Transistors were used in place of vacuum tubes. (invented at AT&T Bell lab in 1947) ƒ Small in size ƒ Lesser power consumption and better performance
Computer Organization 1. Introduction
ƒ Lower cost ƒ Magnetic ferrite core memories were used as main memory which is a random-access nonvolatile memory ƒ Magnetic tapes and magnetic disks were used as secondary memory ƒ Hardware for floating point arithmetic operations was developed. ƒ Index registers were introduced which increased flexibility of programming. ƒ High level languages such as FORTRAN, COBOL etc were used - Compilers were developed to translate the high-level program into corresponding assembly language program which was then translated into machine language. ƒ Separate input-output processors were developed that could operate in parallel with CPU. ƒ Punched cards continued during this period also. ƒ 1000 fold increase in speed. ƒ Increasingly used in business, industry and commercial organizations for preparation of payroll, inventory control, marketing, production planning, research, scientific & engineering analysis and design etc.
Third Generation (System 360 Mainframe from IBM, PDP-8 Mini Computer from Digital Equipment Corporation) ƒ ICs were used ƒ Small Scale Integration and Medium Scale Integration technology were implemented in CPU, I/O processors etc. ƒ Smaller & better performance ƒ Comparatively lesser cost ƒ Faster processors ƒ In the beginning magnetic core memories were used. Later they were replaced by semiconductor memories (RAM & ROM) ƒ Introduced microprogramming ƒ Microprogramming, parallel processing (pipelining, multiprocessor system etc), multiprogramming, multi-user system (time shared system) etc were introduced. ƒ Operating system software were introduced (efficient sharing of a computer system by several user programs) ƒ Cache and virtual memories were introduced (Cache memory makes the main memory appear faster than it really is. Virtual memory makes it appear larger) ƒ High level languages were standardized by ANSI eg. ANSI FORTRAN, ANSI COBOL etc ƒ Database management, multi-user application, online systems like closed loop process control, airline reservation, interactive query systems, automatic industrial control etc emerged during this period.
Fourth Generation (Intel’s 8088,80286,80386,80486 .., Motorola’s 68000, 68030, 68040, Apple II, CRAY I/2/X/MP etc) ƒ Microprocessors were introduced as CPU– Complete processors and large section of main memory could be implemented in a single chip ƒ Tens of thousands of transistors can be placed in a single chip (VLSI design implemented) ƒ CRT screen, laser & ink jet printers, scanners etc were developed. ƒ Semiconductor memory chips were used as the main memory. ƒ Secondary memory was composed of hard disks – Floppy disks & magnetic tapes were used for backup memory ƒ Parallelism, pipelining cache memory and virtual memory were applied in a better way ƒ LAN and WANS were developed (where desktop work stations interconnected) ƒ Introduced C language and Unix OS ƒ Introduced Graphical User Interface Computer Organization 1. Introduction
3 ƒ Less power consumption ƒ High performance, lower cost and very compact ƒ Much increase in the speed of operation
Fifth Generation (IBM notebooks, Pentium PCs-Pentium 1/2/3/4/Dual core/Quad core.. SUN work stations, Origin 2000, PARAM 10000, IBM SP/2) ƒ Generation number beyond IV, have been used occasionally to describe some current computer system that have a dominant organizational or application driven feature. ƒ Computers based on artificial intelligence are available ƒ Computers use extensive parallel processing, multiple pipelines, multiple processors etc ƒ Massive parallel machines and extensively distributed system connected by communication networks fall in this category. ƒ Introduced ULSI (Ultra Large Scale Integration) technology – Intel’s Pentium 4 microprocessor contains 55 million transistors millions of components on a single IC chip. ƒ Superscalar processors, Vector processors, SIMD processors, 32 bit micro controllers and embedded processors, Digital Signal Processors (DSP) etc have been developed. ƒ Memory chips up to 1 GB, hard disk drives up to 180 GB and optical disks up to 27 GB are available (still the capacity is increasing) ƒ Object oriented language like JAVA suitable for internet programming has been developed. ƒ Portable note book computers introduced ƒ Storage technology advanced – large main memory and disk storage available ƒ Introduced World Wide Web. (and other existing applications like e-mail, e Commerce, Virtual libraries/Classrooms, multimedia applications etc.) ƒ New operating systems developed – Windows 95/98/XP/…, LINUX, etc. ƒ Got hot pluggable features – which enable a failed component to be replaced with a new one without the need to shutdown the system, allowing the uptime of the system to be very high. ƒ The recent development in the application of internet is the Grid technology which is still in its upcoming stage. ƒ Quantum mechanism and nanotechnology will radically change the phase of computers.
