computer




- A computer is a device that accepts information (in the form of digitalized data) and manipulates it for some result based on a program or sequence of instructions on how the data is to be processed. Complex computers also include the means for storing data (including the program, which is also a form of data) for some necessary duration. A program may be invariable and built into the computer (and called logic circuitry as it is on microprocessors) or different programs may be provided to the computer (loaded into its storage and then started by an administrator or user). Today's computers have both kinds of programming.
Most histories of the modern computer begin with the Analytical Engine envisioned by Charles Babbage following the mathematical ideas of George Boole, the mathematician who first stated the principles of logic inherent in today's digital computer. Babbage's assistant and collaborator, Ada Lovelace, is said to have introduced the ideas of program loops and subroutines and is sometimes considered the first programmer. Apart from mechanical calculators, the first really useable computers began with the vacuum tube, accelerated with the invention of the transistor, which then became embedded in large numbers in integrated circuits, ultimately making possible the relatively low-cost personal computer.

Modern computers inherently follow the ideas of the stored program laid out by John von Neumann in 1945. Essentially, the program is read by the computer one instruction at a time, an operation is performed, and the computer then reads in the next instruction, and so on. Recently, computers and programs have been devised that allow multiple programs (and computers) to work on the same problem at the same time in parallel. With the advent of the Internet and higher bandwidth data transmission, programs and data that are part of the same overall project can be distributed over a network and embody the Sun Microsystems slogan: "The network is the computer."

Parts of a computer

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 illustration below shows the most common hardware in a desktop computer system. Your system may 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 a peripheral 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.


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, and 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.


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 floppy disks "floppy"? Even though the outside is made of hard plastic, 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.
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.


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.

You can also use your keyboard to perform many of the same tasks you can perform with a mouse. For more information, see Using 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 LCD (liquid crystal display) monitors. Both types produce sharp images, but LCD monitors have the advantage of being much thinner and lighter. CRT monitors, however, are generally more affordable.


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 materials. 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.


Speakers
Speakers are used to play sound. They may be built into the system unit or connected with cables. Speakers allow you to listen to music and hear sound effects from your computer.

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.

ALU
Abbreviation of arithmetic logic unit, the part of a computer that performs all arithmetic computations, such as addition and multiplication, and all comparison operations. The ALU is one component of the CPU (central processing unit).

What is a Computer Virus?


What are Computer Viruses?

Computer viruses are programs written by "mean" people. These virus programs are placed into a commonly used program so that program will run the attached virus program as it boots, therefore, it is said that the virus "infects" the executable file or program. Executable files include Macintosh "system files" [such as system extensions, INITs and control panels] and application programs [such as word processing programs and spreadsheet programs.] Viruses work the same ways in Windows or DOS machines by infecting zip or exe files.

A virus is inactive until you execute an infected program or application OR start your computer from a disk that has infected system files. Once a virus is active, it loads into your computer's memory and may save itself to your hard drive or copies itself to applications or system files on disks you use.

Some viruses are programmed specifically to damage the data on your computer by corrupting programs, deleting files, or even erasing your entire hard drive. Many viruses do nothing more than display a message or make sounds / verbal comments at a certain time or a programming event after replicating themselves to be picked up by other users one way or another. Other viruses make your computer's system behave erratically or crash frequently. Sadly many people who have problems or frequent crashes using their computers do not realize that they have a virus and live with the inconveniences.

What Viruses Don't Do!

Computer viruses can not infect write protected disks or infect written documents. Viruses do not infect compressed files, unless the file was infected prior to the compression. [Compressed files are programs or files with its common characters, etc. removed to take up less space on a disk.] Viruses do not infect computer hardware, such as monitors or computer chips; they only infect software.

In addition, Macintosh viruses do not infect DOS / Window computer software and vice versa. For example, the Melissa virus incident of late 1998 and the ILOVEYOU virus of 2000 worked only on Window based machines and could not operate on Macintosh computers.

One further note-> viruses do not necessarily let you know they are present in your machine, even after being destructive. If your computer is not operating properly, it is a good practice to check for viruses with a current "virus checking" program.

How do Viruses Spread?


Viruses begin to work and spread when you start up the program or application of which the virus is present. For example, a word processing program that contains a virus will place the virus in memory every time the word processing program is run.

Once in memory, one of a number of things can happen. The virus may be programmed to attach to other applications, disks or folders. It may infect a network if given the opportunity.

Viruses behave in different ways. Some viruses stay active only when the application it is part of is running. Turn the computer off and the virus is inactive. Other viruses will operate every time you turn on your computer after infecting a system file or network.

How to Prevent a Virus Invasion!

Load only software from original disks or CD's. Pirated or copied software is always a risk for a virus.
Execute only programs of which you are familiar as to their origin. Programs sent by email should always be suspicious.
Computer uploads and "system configuration" changes should always be performed by the person who is responsible for the computer. Password protection should be employed.
Check all shareware and free programs downloaded from on-line services with a virus checking program.
Purchase a virus program that runs as you boot or work your computer. Up-date it frequently.


Trojan Horses

A trojan horse is not a virus. It is a program that you run because you think it will serve a useful purpose such as a game or provides entertainment. Like a "trojan horse" it serves not as it claims, but to damage files or perhaps plants a virus into your computer. A trojan horse does not replicate or spread like a virus. Most virus checking programs detect trojan horses.