Kinds of computers
There are six types of computers: personal computers, mainframes, laptop computers, mini computers, super computers and embedded computers.
A "desktop computer" is a small machine that has a screen (which is not part of the computer). Most people keep them on top of a desk, which is why they are called "desktop computers." "Laptop computers" are computers small enough to fit on your lap. This makes them easy to carry around. Both laptops and desktops are called personal computers, because one person at a time uses them for things like playing music, surfing the web, or playing video games.
There are bigger computers that many people at a time can use. These are called "Mainframes," and these computers do all the things that make things like the internet work. You can think of a personal computer like this: the personal computer is like your skin: you can see it, other people can see it, and through your skin you feel wind, water, air, and the rest of the world. A mainframe is more like your internal organs: you never see them, and you barely even think about them, but if they suddenly went missing, you would have some very big problems.
There is another type of computer, called an embedded computer. An embedded computer is a computer that does one thing and one thing only, and usually does it very well. For example, an alarm clock is an embedded computer: it tells the time. Unlike your personal computer, you cannot use your clock to play Tetris. Because of this, we say that embedded computers cannot be programmed, because you cannot install programs like Tetris on your clock. Some mobile phones, automatic teller machines, microwave ovens, CD playersand cars are examples of embedded computers.
Computers store data and the instructions as numbers, because computers can do things with numbers very quickly. These data are stored as binarysymbols (1s and 0s). A 1 or a 0 symbol stored by a computer is called a bit, which comes from the words binary digit. Computers can use many bits together to represent instructions and the data that these instructions use. A list of instructions is called a program and is stored on the computer's hard disk. Computers work through the program by using a central processing unit, and they use fast memory called RAM as a space to store the instructions and data while they are doing this. When the computer wants to store the results of the program for later, it uses the hard disk because things stored on a hard disk can still be remembered after the computer is turned off.
An operating system tells the computer how to understand what jobs it has to do, how to do these jobs, and how to tell people the results. Millions of computers may be using the same operating system, while each computer can have its own application programs to do what its user needs. Using the sameoperating systems makes it easy to learn how to use computers for new things. A user who needs to use a computer for something different, can learn how to use a new application program. Some operating systems can have simple command lines or a fully user-frendly GUI.
source:wikipedia
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