Sonic's Desktop

Graphical Output Devices

In our last few editions, we've been going deep into various types of computer hardware. We first categorised the hardware components that we find in a computer system as input devices, output devices, systems unit and secondary storage.

Then we went in to specific details of various input devices that are available today. We started our exploration about output devices in our previous edition, and today, let's have a look at a particular type of output devices

 graphical output devices.

These output devices are the most common output devices you see today. These are none other than the 'computer display monitors' or in simple terms, 'monitors.' The functions of these will be very familiar to you because you are familiar with television.

This means that monitors give you the opportunity to view what is going on in your computer in a graphical mode. This is done by letting you see images or pictures which are generated by the computer. These pictures may change very fast or slowly depending on the situation.

Since you are clear about the output produced through the monitor, let us look at some technologies used in monitors which have their own advantages and disadvantages.

Today we'll take a look at CRT monitors, which are the most common monitors seen around.

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Cathode Ray Tube (CRT)

You may not be familiar with what a cathode ray tube is right now, but you must know that the big TV sets at your homes are generally in this category. We will simply see how images appear on the screen of a CRT monitor.

These monitors have what is called a picture tube. It is because of this tube that the normal TVs become large towards the back of the TV. The back of this tube is a cathode. This means it is negatively charged.

The electron guns produce electrons, and they are shot on to the screen from behind. The screen is coated with a pattern of dots that glow when struck by electrons. Each cluster of three dots(one of each in the colours, red, blue and green), is known as one 'pixel'.

The screen is divided in to tens and thousands of such pixels. So, you would understand that the smaller the pixel, the more detail there would be in the picture, making it more realistic. This is determined by the screen resolution, which refers to the number of distinct pixels in each dimension that can be displayed.

The pictures of a monitor undergo change very quickly and it is known as 'refreshing'. The videos and other moving images can be seen when the pictures generated move rapidly. The number of times that the electron gun redraws the entire image in one second is called the 'refresh rate'.

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Advantages of CRT monitors

* CRT monitors run at a high resolution.

* They can produce a very dark black and the highest contrast levels normally available. They are suitable for using even in dimly lit or dark environments.

* CRTs produce the very best colour and gray-scale, and are the reference standard for all professional calibrations.

* CRTs are less expensive than comparable displays using other display technologies.

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Problems with CRT monitors

* At relatively low refresh rates, the one who is looking in to the screen may feel a 'flicker' in the image. This may cause eyestrain and nausea.

* If the same image is left to be displayed for a long time, it can permanently embed that image to the phosphor coating of the screen. This is known as 'screen burn'. The result of this is seeing 'ghostly' images of the picture even when the screen has changed, or is even turned off.

* Since the picture tube is quite long, this sort of monitor takes up a considerable amount of space.

* Not suitable to use in very bright environments.

* They consume a lot of power and produce a lot of heat.

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Sonic's Q&A

Q - What is a vacuum tube?

A - A device which could amplify, switch or modify a signal by controlling the movement of electrons in a vacuum (evacuated) region.

Q - When were vacuum tubes used in computers?

A - During the first generation of computers (1939-1954).

Q - What was the major invention that took place in the second generation of computers?

A - The invention of the 'transistor'.

Q - Who invented the transistor?

A - It was invented by Schockley, Bardeen and Brattain at Bell Labs.

Q - Who invented the 'Integrated Circuit'?

A - Jack Kilby of Texas Instruments.

Q - What is the importance of the fourth generation?

A - The invention of the microprocessor.

Q - What was the world's first sealed hard disk?

A - 'Winchester' made by IBM in 1973.

Q - Who started the production of computer game cartridges?

A - Nintendo of Japan.

Q - How can the entire computer be categorised?

A - Hardware, Software and Liveware.

Q - What is hardware?

A - All what you can see and feel of a computer. In other words, the physical parts of the computer.

Q - What is software?

A - The means by which hardware communicate with each other. Simply speaking these are programmes that control the computer.

Q - What is Liveware?

A - The people who are associated with operating the computer.

Aravinda Dassanayake