COMPUTER NOTES

Introduction

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P.C. is a machine design for personal use. It consists of

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Monitor
System box
Mouse
Keyboard

And Various drive (CPU) Motherboard and variety of electronic cards

These components form the main body of computer system. But other system can be connected to it e.g. scanner, printer, camera and joysticks. These external devices are called peripheral devices The part of a computer system that you are able to see

Monitor on which information is displayed
System box-unit in which main components are stored these includes,
CPU,
Memory, Drives and power supply.

CD-Rom or DVD drive which allows the system to read the respective disc on which most software is now supplied. CD-Rom can hold 650 megabytes of data. DVD can hold approximately 1000 million gegabytes. Both types of discs enables you to read large volumes of personal stored information but you can not change the data

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There are drives which allows you to store new information on them. They are called CD-R(Compact disc Recordable) and CD-RW (Compact disc Read Write)

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Zip-drive is a means of storing data on small discs Floppy disc hold 100-250 mgb. But are not interchangeable with Floppy disc
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Floppy disc drive is a standard way of moving information between computers. A floppy disc is a small magnetic disc on which a small amount of data can be stored.
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Part of the computer which is �hidden� inside the system unit

�CPU is the brain of the computer. The speed of the CPU is measured by its clock speed e.g. Pentium III 700 MHz, 800 MHz, AMD Athlon and Celeron 300. This shows how many millions times per second a C.P.U carries out basic operation. It is measured in Megahertz.

A graphic card. that controls the display of image on the monitor
Expansion slot which are placed for you to add extra electronic cards to the system in order to increase its functionality, e.g. sound.
Modem which allows computer to communicate with other modem

Motherboard is a circuit board, which all the other components connect so that they can communicate with each other Chipsets, which is a group of chips on motherboard, which control the main function of the computer, i.e., allowing the CPU to communicate with Memory, Hard disc and cards. � Random Access Memory (R.A.M.), which is the working memory of the computer, it is lost when you switch off the machine.

Output devices

The two main output devices are Monitor and Printers. A monitor is a Visual Display Unit (V.D.U.) is attached to almost all type of computers. Printers are a very important means of organizing the output of computer information by printing the data paper.

There are three main types of printers

Monochrome Laser Printer. It uses block magnetic toner very similar to that used in photocopies to produce text and images on paper. A drum is used to transfer the toner to paper by charging it with static electricity to repel the toner. Laser printers are widely used in the workplace because of their high quality and speed output
Monochrome Color Inject Printer. Work by squirting small drops of ink on to the page. They provide both black and white and color. Ink is stored in cartridges, which are simple to replace, are widely used in the home and business
Color Laser Printers are relatively expensive and normally reserved for large users and specialists (e.g. Printers and Graphic Designers). The quality of all printers is normally presented in terms of print resolution expressed in Dots Per Inch (DPI) and speed in terms of Pages Per Minute (PPM).

Input devices.

It includes Keyboard and Mouse although there are a wide range of other devices including different type of Scanner e.g. Flatbed, Sheetbed and pen pointing device (e.g. light pens, joysticks, touch pad ,roll balls and speech input). Mouse is commonly used at controlling on screen pointing the pointer allow object e.g. Icon buttons to be chosen in order to initiate an action. There are different types of Mouse one with two or three buttons, but mouse with two buttons are commonly used. In most cases the movement and button press are communicated to the computer through a cable connected to a port but some mice use infra-red senders and receiver. Some Mice include a roller bar in order to allow them to scroll the display

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Type of scanners.

Flatbed Scanner for inputting illustration and text into computer. To scan text requires OCR Optical Character Reading software that allows the text to be imported into word processor so that it can be manipulated.
Sheet Scanner primarily use to scan text on documents.
A Pen Scanner is rather like highlighting pen in that lines of text can be scanned and stored in the devise. The text is then transferred from the pen to the computer by attaching a cable or infrared.

Computer Memory.

Random Access Memory (RAM). This is the working memory in which the computer carries its function while it is switch on. It only exist while machine is on, if the machine is switch off so is the memory. The more the RAM the faster the computer will operate. Read Only Memory (R.O.M) is the permanent memory built into the silicon chip structure inside the computer. It is not lost when power is off. Storage. This is where information and program are stored as magnetic pattern on a hard disc. Flash memory card e.g. in a digital cameraCP-RW DVD RAM or Floppy

When the computer is switched on it uses R.O.M to provide the basic instruction to set up the computer. It works on problem in RAM and store the result on the hard disc .CD-R CPRW Magnetic tape or Floppy disc

Memory is measured in bytes. A byte is sufficient memory to store one character e.g. letter or a number. There is a smaller memory called a bit. A byte equals eight bits. A bit is essentially enough memory to store a single item of binary arithmetic that�s one or zero

Modern computers are often describe in terms of their memory (e.g. 128 megabyte of RAM). 1.44 Megabytes of Floppy disc (about 1.440.000 bytes)

Main frame computer

The first computer were Mainframes. They were very large and powerful machines

They required a team of specialists to operate and program them. �
They occupied an entire floor of a large building. �
They undertook large computational task such as keeping a/c for multinational companies or government department. �
People communicate with Mainframe computer from dumb terminal which look similar to PC but do not have any processing power of their own. �
Mainframe can handle communication with many hundreds of users simultaneously with many of them working in a remote site. �
Mainframe can run many different programs at the same time

Mini Computers �

Are used with individual organization to undertake the function required by the enterprises e.g. accounts and storage of customer information. � They are more robust than Mainframes so they are used in Industrial application or in location where Mainframe would be uneconomical. � A single Mini computer can be linked together to extend the network � Both Mainframes and Mini computers are centralized system where the individual terminal is not able to work independently. � The PC changed this configuration since they are stand-alone machine PC can act as terminal but in order to do this they must run emulation software which make computer behave like a dumb terminal. dumb terminal is a monitor and keyboard which is connected to Mainframe on Mini-computers. It has no local processing. Power is therefore deemed to be dumb

Local Areas Network (LANS).

A computer network is a group of computers linked by cables so that they can communicate with each other in order to resources Small single organization are normally called LANs L.A.N is widely used in many different organizations from small business to school. L.A.N allows you to minimize the return on your investment in computer equipment e.g.

Sharing expensive equipment e.g. printers
Access to common files and resources
Communication between users through the use of e-mail

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