Wednesday, January 9, 2008

COMPUTER


Computer is a programmable machine. It accept user-supplied data and instructions, store data and instructions perform mathematical and logical operations (i.e., execute the instructions), and output the result according to user specifications. There are two principal characteristics of a computer are:
It responds to a specific set of instructions in a well-defined manner.
It can execute a prerecorded list of instructions (a program).
Modern computers are electronic and digital. The actual machinery -- wires, transistors, and circuits -- is called hardware; the instructions and data are called software.
COMPUTER HARDWAREHardware is refers to the physical devices a computer system. Hence, the input, storage, processing, control and output devices are hardware.There are so many hardware manufactures. The detail of hardware devices and comparison of hardware manufactures is given below.

SCANNER

Scanners have become more popular as the price has fallen within the range of the average person. Scanners allow one to transfer pictures and photographs to a computer. A scanner 'scans' the image from the top to the bottom, one line at a time and transfers it to the computer as a series of bits or a bitmap. It is then possible to take the image and annotate or change it in a graphics package, send it out as a fax or print it. The two most common types of scanners are flatbed and handheld scanners. With flatbed scanners, the picture sits on a flat surface - the bed of the scanner - and the scanner moves across the bed. With handheld scanners, the picture is fed, by way of rollers, underneath the scanner.

SYSTEM CASES

The system case is the box or outer shell that houses the microchips and circuitry that run the computer. While it may seem inconsequential, the case actually performs several important functions for your PC, including protection for the computer circuits, cooling, and system organisation. In addition, the system case is normally purchased together with the system power supply, and must also be matched with the size, shape and electrical requirements of your motherboard. Therefore, it has an impact on your options with these important components as well. Thought also needs to be given as to whether the case has sufficient room to expand or add components at a later stage. Desktop cases usually sit under the monitor while towers sit beside. Notebook computers may have room to expand depending on the type of computer. Most modern Notebooks have a connection called a PCMCIA port that allows expansion or connection to exterior peripheral devices.

MOUSE

Until the invention of software using GUI's, the keyboard was the only way that most people input information into their PCs. Mice are used in graphical environments to let users provide simple "point and click" instructions to the computer. The main advantage of a mouse over the keyboard is simplicity. There are also some operations that are much easier to perform with a mouse than a keyboard (such as picking an item on a screen or choosing from a list of options). Generally, if the mouse has two buttons, the left one is used to select objects and text and the right one is used to access menus. If the mouse has one button (such as with Mac PC's), it controls all the activity. A mouse with a third button can be used by specific software programs. Track balls and touch-pads are variations on the mouse that are used with laptops.

MOTHERBOARD

The motherboard is the base of the modern computer system. If the processor is the "brain" of the computer, then the motherboard is the central nervous system and circulatory system, plus much more, all rolled into one. The motherboard is the main circuit board in the computer where everything comes together. This is where you plug in your processor, memory, cache, video card and other cards. It is also where you connect your peripherals.

RAM

Random Access Memory or RAM is the memory that the computer uses to temporarily store the "active" information as it is being processed. When the computer is turned on, the memory is empty. Each program or data file that is loaded uses part of the system memory. When a program is closed, the memory is freed up for other uses. Generally, the more memory the system has, the more things can be done with it simultaneously. Increasing the amount of memory in the system also improves performance in most cases. Most computers use RAM called SIMM's (Single Inline Memory Modules). Older computers use 30 pin SIMM's while modern computers use 72 pin SIMM's. The latest technology now being made available are 168 pin DIMMs (Dual Inline Memory Modules). It is interesting to note that one of the first home computers used 64 kilobytes of RAM memory. Today's modern computers need a minimum of 64 MB (MegaBytes) to run Windows 2000. In most computers the memory can be expand with 4 Mb, 8 Mb, 16 Mb, 32 Mb, 64 Mb or recently even 128 Mb chips depending on the processor you have and the type of memory your computer uses. Usually the computer can only use the same types of chip so if your computer has 4 Mb chips you have to use 4 Mb chips. When you want to expand your memory you must remove them all and replace them with larger chips.

DISPLAY SCREEN

In simple terms, the monitor is a specialised high-resolution screen, similar to a high-quality television, that displays information relating to what processing is happening inside the computer. This is referred to as outputting information. When the computer finishes processing information or requires more information, a message or prompt will be displayed on the screen. Monitors come in many types - from the simple monochrome (one colour) screen to full colour screens - and sizes. The most popular sizes for monitors are 14", 15", 17", 20" and 21". This number represents the diagonal width, in inches, from one corner of the screen to the opposite corner, and is the monitor's nominal size. The viewable size is generally less than this. Most desktop computers use a monitor with a cathode ray tube (CRT) while most notebooks use a liquid crystal display (LCD) monitor. The information displayed on the monitor is controlled by the computers video or graphics card.

PRINTER

The printer takes the information on the screen and transfers it to paper or what is referred to as a hard copy. There are many different types of printers with various levels of quality. The three most common types of printer are dot matrix, inkjet and laser. Dot matrix printers work like a typewriter transferring ink from a ribbon to paper with a series or 'matrix' of tiny pins. This was one of the first types of printers but despite its relatively slow speed is still used today in applications were a carbon copy of the printed output is required. Ink jet printers work by spraying a fine stream of ink from a cartridge directly onto the paper. This type of printer is the most popular choice for home applications because of its relatively low price. Laser printers use the same technology as a photocopier using heat to transfer toner onto paper. High speeds and the high quality of print make this type the most popular choice for business applications.

CENTRAL PROCESSING UNIT

The CPU is a silicon chip containing extremely complicated and sophisticated electronic circuits. It is often thought of as the "brain" of a computer and is at the base of all the tasks the PC performs. It processes all the instructions coming in from input devices and those going out to output devices. The Pentium series processors, made by Intel, and the Athlon series processors, made by Advanced Micro Devices (AMD), are currently the most commonly available. Before this, Intel produced the 80286, 386, and 486 chips for DOS based systems. Many people consider the 80286 as the advent of home computing, as this was the processor that made computers available to the average person. The Power PC made by Motorola is currently the most common for Mac based systems. Before this there were 68000, 68020, 68030, 68040. The processors' clock speed gives an indication of the speed at which the PC operates. Compared to some of the first computers which operated at below 30 megahertz (MHz) today's chips begin at 75 MHz and go up to 1.5 GHz (check your local computer store for the latest speed).

KEYBOARD

The keyboard is used to type information into the computer, or input information. Although there are many different keyboard layouts and sizes, the Enhanced 101-keyboard, introduced by IBM in 1986, has become the de-facto standard. Even today's ergonomically designed Windows keyboards are based on the original 101 layout. They simply have additional keys, which facilitate Internet browsing and Windows operations. Notebooks or Laptops have embedded keys accessible by special keys or pressing key combinations.

CD/DVD

CD drives use compact disks, similar to the ones that hold music, to store information. A few years ago, CD drives were only available as ROM drives or Read Only Memory drives. These drives could only read information from a CD but not write to them. Recently, however, writeable CD drives have become less expensive and readily available to the average computer user. These drives allow one to write to a CD, thus allowing one to back-up and store vast quantities of information to a single disk. CD-ROMs are currently the most popular way that computer companies distribute applications and games, and are ideal for multimedia information like videos, music and large graphics files.

MODEM

A modem is used to transfer information through telephone lines. The term stands for modulate and demodulate which means to change the signal from digital, which computers use, to analogue, which telephones use and then back again. Modems are measured by the speed that the information is transferred. The measuring tool is called the baud rate. Originally modems worked at speeds below 2400 baud but today 14,400 is the minimum and speeds of 56,000 are common. Modems also use error correction that corrects for line noise on the telephone system by constantly checking whether the information was received properly or not and compression that allows for faster data transfer rates.