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Think of a computer as a human brain. Your brain is a memory sponge. It contains a lifetime of memories that cause us to act or react based on inputs. Inputs come through our 5 senses. If you see and smell hot suya burning on the grill (inputs) you know how to react based on previous experiences (memory - " I HAVE TO EAT O!).

A set of miniaturized circuits which represents the working memory of the computer. This is where application programs (software) can be loaded from the outside and then executed. The larger the RAM the better. For example a typical single user computer system may contain approximately 1,000,000,000 bytes of RAM.
(This is often abbreviated as 1000MB RAM.)

The computer's brain consists of the RAM and the CPU. The CPU and RAM work together as the computer's "brain". Each day when we start up the computer one of the first tasks will be to fill RAM with instructions to give it an ability to do work. This work may be in the creation of documents or tracking accounting data.

You control which instructions will go into the computer's brain. You control the sets of experiences you will provide the computer. Once in RAM, the computer will evaluate inputs from many devices and react. The most typical input device is a keyboard. As you type commands, the computer evaluates them. Based on the set of instructions within its RAM, it will follow some action: print a document, calculate, send information over a telephone line, etc.

At some later point you may empty the computer's brain and install a different set of instructions, thus giving it a different ability.
The RAM is emptied when the computer is turned off - thus it is often called "volatile" memory. WHAT YOU SEE ON YOUR COMPUTER MONITOR IS ACTUALLY IN RAM ONLY - a temporary storage location. To make it permanent we "save" it or "write" it to a hard drive or removable storage such as flash drive or SD card etc. These devices are non volatile storage - they do not require electricity to keep information within them.

Each time the computer is turned off, all information within RAM is lost. RAM is called volatile memory because of the electricity requirement.


This is a special section of memory that contains instructions which are activated each time the computer is turned on. These instructions are set at the factory and cannot be changed - thus, they can only be "read", not written to. ROM instructions perform equipment checks and initialization of the computer prior to each use. Furthermore, information on a ROM can not be altered or deleted.

However, new types of ROM (e.g DVD-RW, BD-RW etc.) can have some of the content on them edited, even deleted.

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Think of disks as cassettes. You can record information on a cassette that can be replayed indefinitely and if desired, recorded over. Flash and Hard Disks operate in a similar fashion. We record (Save) data we have created - like a document - onto the disk. Then, hours, days, or months later we can play back (Retrieve) the document in the computer to alter or print out.

Storage devices are non-volatile in nature because they will retain their information without the use of electricity and can be grouped into any of the following: magnetic, solid state, optical.

Magnetic disks (made up of metals mostly) works in the same fashion but spins in a circle like a music record rather than moving in a straight line like recording tape - magnetic impressions are placed on the tape and can be later replayed. Hard disks are typical examples of magnetic storage.

Solid state disks are rather chip-like (mostly made of semiconductors and plastics) type of storage that have relatively smaller capacity(ies) than the magnetic storage. They are less likely to fail due to the nature of materials there are made of. Examples include flash drives, memory cards (SD/MiniSD/MicroSD/MMC/XD) etc.

Optical storage better grouped as ROM require a drive with a lens to write/read their content. They are made from plastics and can be any of CD (with 700MB capacity), DVD (with 4.7GB capacity; 9.4GB if it is a Double Layer) or Blu-Ray Disc with 25GB capacity; 50GB if it is Double Layer. Since optical disks have features of ROM, information stored on it is read only and can not be edited. However, some of their content on these discs can be edited and deleted when there are having the designation -RW (meaning rewritable).

When you format a disk you ask the computer to inspect the magnetic surface of the disk ( if it is a hard disk drive) for any errors, prepare it for use by future data and create an index such as file allocation table (FAT) or new technology file system (NTFS) which is like a card index for a large library of books. Formatting a disk is a little like taking a blank piece of paper and using a pencil and ruler to turn it into graph paper with both horizontal and vertical lines. What was blank before now has little cells or file drawers which can hold information.

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Since we have covered data storage lets move to data input.

Two primary input devices are key to getting data into a PC. The keyboard and the mouse.

Input device that lets you enter data into the computer. The layout is similar to the standard QWERTY typewriter keyboard. However, there are many extra special keys that are defined by the software you are running.

(ii) MOUSE
Hand operated pointing and selection device which serves as alternate input to the keyboard. It is very useful for Graphical User Interface (GUI) Applications such as Windows, etc., which is rolled or moved across the desktop to position a cursor or pointer on the computer screen.
The mouse also contains several buttons to help select items on data on the monitor screen. A mouse was initially an optional device, but it is becoming difficult to work without it, with the spread of Windows based systems.

Lets move on to the specialty input devices like the scanner and the Digital camera.

A scanner converts text and images to digital information. This text and images can be from a variety of sources such as magazines, photographs, articles, scientific diagrams, etc. The scanner creates a digital image from your photograph or drawing, for use in graphics, DeskTop Publishing or Presentation applications.
There are different types of scanners like Hand scanner, flatbed scanner and the multifunction scanner/fax/printer/copier. The flatbed scanner provides a larger scanning area than the other scanners and is the usually more expensive.

The Digital Camera produces the same result as a Scanner. Any pictures taken are transferred straight to the computer, i.e. in the form of a graphics image suitable for image editing or DeskTop Publishing applications. It eliminates the need for film.

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Another introductory topic is that of output devices such as a monitor, printer or plotter.


A plotter is a device which uses a motor to move pens or drawing implements in tightly controlled horizontal and vertical motions on a piece of paper or film. The computer can control a plotter to combine on one piece of paper differing pen colors and text and pictures stored within the computer. Computer plotter can be purchased with flat table or flat bed configurations or in models which move the pen(s) back and forth with gears that also drive the paper movement at the same time.


The printer is probably the most common and useful output device attached to your computer. There are many types of modern computer printer with differing speeds and capabilities. The most common printer is the Dot
matrix printer which provides characters made up from tiny dots of ink on paper. Line printers (usually with Mainframe computers or Minicomputers) print entire lines of text in one sweep then move to the next line and are thus very fast. Ink jet printers produce characters made from individual dots of ink sprayed onto the paper.
The ink jet printer squirts individual dots of ink onto the paper to form letters or other characters. A high quality paper is necessary since the wet ink can smear if not carefully handled. Although with the most recent models, ordinary paper can also be used. The Colour print facility is also now standard with most inkjet printer.
Finally, laser printers use a rapidly scanning laser to sensitize a polished drum with an entire page of information quickly and look and work roughly like an office copier. The first two printers are classified as impact printers since something strikes the paper while the later two are non impact printers.

The laser and ink jet printers are becoming more popular due to rapid speed of printing and quiet mode of operation.

The laser printer is used for quickly producing one page of text at a time. In operation, the laser scans a polished drum with an image which is then dusted with dark toner particles which stick to the exposed areas made sensitive by the laser. Paper is then placed in contact with the drum and the toner is transferred to the page and is finally fused with heat to "fix" or seal the toner particles to the page.
Of the Microcomputer printers, the Laser is the most expensive in terms of purchase price, maintenance cost and consumable cost.

Dot matrix printers are common and affordable alternatives for many small offices, home computer hobbyists or organizations with voluminous printing requirements (e.g. statements of accounts for banks). The Dot matrix is additionally designed for use with continuous flow paper, as well as typical single sheet paper.
Dot matrix usually operates in varying modes of draft and letter quality. In draft mode, the printer speed is faster, with draft quality. Letter quality is slower with higher quality.
Dot matrix printers produce letters via small pins which strike the ink ribbon and paper to produce print which can be jagged looking. Nine pin dot matrix printers produce somewhat rough looking letters while 24 pin dot matrix printers produce crisper, fully-formed letters. The Dot matrix printer strikes the paper through a ribbon to transfer ink to the printed page.

Connecting a printer via a cable to the computer is always done through one of two plugs (or interfaces) on the back of the computer. One type of interface (computer plug) is serial, the other called parallel.
The most commonly used interface for printers today is the parallel interface but serial interface printers do exist. What is the difference? Recall that there are eight bits (computer dots and dashes) to a byte (or computer word). The serial interface has each bit sent one at a time to the printer - like men in single file at the supermarket checkout counter. The parallel interface sends all eight bits at once - like eight men all entering eight supermarket counters at once. Each interface is different, the printer manufacturer will tell you which interface to use, i.e. serial or parallel.
Frequently, modems or mouse devices use the serial interface leaving the printer to the parallel interface.


We have talked about output to paper, next let's briefly discuss output to a monitor or screen. The monitor is a television like device that the computer uses to communicate with you. The monitor or video display works much like your television - some older home computers still use a TV. An old term for a monitor is the cathode ray tube or CRT. Monitors differ in the sharpness or resolution they can display. On the low end of the resolution spectrum is the monochrome (single color) monitor frequently available in either green or amber screens. Next is the color RGB monitor (RGB stands for Red, Green and Blue) which displays low resolution color dots to make up an image.
Higher resolution is obtained with an EGA monitor (Enhanced Graphics Adapter) and still higher with a VGA (Video Graphics Array) Monitor and even higher with an SVGA (Super Video Graphics Array) Monitor.
Each monitor is matched to work with a circuit card located within the body of the computer. One way to upgrade a computer is to switch both the monitor and display/graphics circuit card to produce a sharper, more colorful image. The dots which make up all images on the monitor screen are called pixels. The smaller the pixels, the higher and sharper the image resolution.
Typically the monitor displays 80 columns (characters) by 25 rows (lines) of information. The initial SVGA cards could only display 16 colours. And then 256 colours. Now some SVGA card can display millions of colours.

Certain devices can act as both input and output devices to the computer. Typical devices mentioned earlier are the disks (floppy, flash, rewritable CDs and hard).


Short for Modulator/Demodulator. A device to send and receive computer output over telephone lines.

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Where is your CPU kept? Don't look for RAM near your mouse. Most of the components are internal, and kept inside a casing. This casing model can be Tower, minitower, desktop or laptop. Inside the casing, there is a power supply unit that takes in the power supplied from the public power supply and steps it down to supply the computer's needs. Also inside the casing is the motherboard, which is a large printed circuit board that all expansion boards plug into.

The motherboard contains the most essential parts of the computer such as the CPU, RAM, ROM, keyboard, speaker and power connections, and other assortment of important parts.
The expansion boards contain special circuits for the monitor (monitor card), disk drives and mouse (multi Input/Output card) and other options such as modem and scanner.


1. RAM is usually more powerful than ROM. COMMENT.

2. What are the differences between the CD disk and the hard disk? In which situation is the CD preferable to the hard disk?

3. What does the message "MEMORY FULL" indicate?

4. Why are certain devices called specialty input devices? What makes them different from the usual input devices?

5. Can printers and monitors be described as Input/Output devices? Explain.

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