What is Computer ?

Wednesday, July 10, 2019


A computer is basically a big calculator PLUS some more. The fact that it can store stuff and that it can do much more complicated calculations a lot quicker than calculators. Computers can perform complex and repetitive procedures quickly, precisely and reliably and can quickly store and retrieve large amounts of data.

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 afterword's so we can see it. Therefore, a computer has four basic functions:





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 appears to be nonsense initials like RAM or CPU.

To keep it simple, first look up any word or technical terms 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 . Second, when you encounter any part of a computer for the first time, find out which of these four functions it is used for.


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.


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 (Central Processing Unit)

The CPU is such an important part of the computer that we often refer to a system by the type of CPU it contains such as Pentium III or 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, the details of conversion and format of data storage will be dealt in detail in later chapters.


Information is stored in a computer in several different ways, but the main two are Primary memory i.e RAM and Secondary memory i.e 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 the computer is turned off so those changes are not lost.

When people talk about the memory of a computer, they almost always mean Primary Memory i.e 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.


There are a number of ways to get data back out of the computer. One of them is right below, and that's the monitor. It has a screen that is similar to a Television 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.

The physical components from which a computer is constructed (electronic circuits and input/output devices) are known as "hardware". Most computers have four types of hardware component: CPU, input, output and memory /storage. The CPU (central processing unit) executes programs ("software") which tell the computer what to do. Input and output (I/O) devices allow the computer to communicate with the user and the outside world. There are several kinds of memory/ storage-fast, expensive, short term memory (e.g. RAM) to hold intermediate results, and slower, cheaper, long-term memory /storage (e.g. magnetic disk and magnetic tape) to hold programs and data between jobs.

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