computer and its parts

INTRODUCTION

This is a very short course about computers. It won’t make you into a computer technician, but it will let you talk to one without thinking they are speaking a foreign language. The computers we are interested in are the general-purpose personal computers like we use at our desk, rather than the specialized computer under the hood of your car, or the big mainframe computers that the IRS uses to keep track of us all.


For our purposes, a computer can be defined as a machine for processing and storing information electronically. To be useful, it must have a way for us to get information into the machine, and some way to get it out afterwards so we can see it. Therefore, a computer has four basic functions:


1. Input

2. Processing

3. Storage

4. Output


Every part of a computer system, and everything it does, is connected to one or more of these basic functions. Computers can seem complex because there are many ways of doing each of these functions, and because everything has a new name, often made up of what appear to be nonsense initials like RAM or CPU.


To keep it simple, first look up any word or technical term you don’t understand. There is a glossary at the back of this course pack with definitions for all the technical terms we use here or that you are likely to hear in talking to technicians. Second, when you encounter any part of a computer for the first time, find out which of these four functions it is used for.


INPUT

The most obvious device for getting information (also called data) into a computer system is the keyboard. Another common input device is the mouse. Almost any time we use a computer we use one or both of these to get text data or instructions into the system. To get large amounts of information into the computer we would probably use a CD (compact disc), a floppy diskette, a modem connected to a phone line, or a network card connected to a network.


With the right sound equipment, a microphone or musical instrument can be used to bring in sound, and a digital camera can download visual information, so these are all being used as input.



KEYBOARD MODEM

JOYSTICK FLOPPY DISKETTES MOUSE
















PROCESSING

If we just put information into the computer and took it out again later, computers could be much simpler. Most of the time though, we want to do something with it or change it in some way. Doing something with it is called processing, or data processing. Most of this takes place in a part called the processor, or Central Processing Unit. This is usually abbreviated to CPU.


The CPU is such an important part of the computer that we often refer to a system by the type of CPU it contains. My office computer is a Pentium III but at home I have an Athlon system. Sometimes you will hear the entire computer cabinet called a CPU.





To help the CPU there is another part that takes over a lot of the arithmetic. It is called the co-processor and also the Numerical Processing Unit or NPU.


The smallest piece of data that a computer can process is called a bit, and each bit will be either a one or a zero. For the sake of efficiency, the computer normally deals with a minimum of 8 bits at a time, and 8 bits together is called a byte. This is an important word to remember, because in working with computers you will hear about bytes frequently, and

also megabytes which is one million bytes. Megabyte is usually abbreviated MB.

STORAGE

Information is stored in a computer in several different ways, but the main two are RAM and hard drive, also called a hard disk.


The hard drive can store huge amounts of information, and it can keep this information when the computer is turned off. The only problem with hard drives is that it takes too long to get the data from them, because the system must wait as the disk spins until the right part of the disk surface comes under the read heads, and then the drive transfers a block of data in sequence.


For information being used at the moment, the system needs to be able to get to any part of that information very quickly. The storage for this information is RAM, which stands for Random Access Memory. Random access means the system can ask for any piece of stored data at random and get it immediately, without waiting for to come up in sequence.


Random access is faster than sequential access. The main reason that computers don’t just store everything in RAM is that information in RAM is lost whenever the power is turned off. So, the computer needs both RAM and disk storage. Everything stored long-term is on the disk, and whatever is needed at the moment is copied into RAM. If changes are made to the data in RAM, the changes must be copied back to the disk before that computer is turned off so those changes are not lost.


When people talk about the memory of a computer, they almost always mean RAM, and not the hard drive or other forms of storage that we haven’t covered yet. Sometimes they will say ‘main memory’ just to be perfectly clear about it.


OUTPUT

There are a number of ways to get data back out of the computer. One of them is right there in front of your face, and that’s the monitor. It has a screen that shows you information from the computer, so it is an output device. The monitor and the parts of the computer that run it are known as video. Another common output device is a printer, which of course puts the computer’s output on paper for you.




Some devices are both input and output, like the floppy diskette mentioned earlier. If you have a modem or network connection, information can go both ways over the line so it’s both input and output. In many cases it is practical to consider input and output together, in which case they are called Input/Output and abbreviated as I/O.