Disk Storage Devices

Disk drives of various kinds are used to store and transfer data files. When data is enterd into a computer it must be saved as a file to preserve it when the computer is switched off: Also software applications need to install files on the main disk drive in the computer in order to run.

The most important type of drivein the computer is the hard disk which is used to store the software and data on which the computer run.

Most computers will also have removable disk drives to install software and backup data files.

Disk performance is principally a question of capacity: how much data can be stored on the disk?
Other factors that influence disk performance are the seek time and the transfer rate.

Hard Disk

The hard disk is usually a device fixed inside the computer. It stores large volumes of data which can be accessed and retrived quickly. The seek time of a hard disk is much lower and the transfer rate much higher than any other type of disk drive.

• Hard disk consist of a number of rigid magnetic disks in a protectives casing. Data is recorded magnetically onto concentric circular tracks each one divides into a number of sectors. Data is accessed by an arm moving over the surface of the disk.

• Hard disk can hold very large amounts of data and are usually very fast in comparison with other storage devices. They very considerably in terms of piece depending on their speed and capacity. Hard disk on sale at the time of writing very in capacity from 80 GB to 750 GB.

• When  you install software the setup istructions indicate the amount of free disk space required for the software to run effectively. Applications typically take up 50-200 MB each though multimedia applications and games can require far more.

• Most hard disk are fixed inside the computer. Removable hard disk are available but tend to be much more expensive.

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Measuring data and storage

A computer process digital data. When you use an input device the signal from the device are converted into a steam of bits the smallest componnents of computer data. Each bit can be in one of two states 1 or 0 with the 1 standing for On and the 0 stand for Off.


Memery and the disks are the components used to store data for processing. The unit used to messure data are bits , bytes , megabytes and gigabytes.

• Bits are combined with sets of eight to form charactors such as letters from the alpherbet. For a example 01000001 is used torepresent the letters A in binary code. This group of eight bits makes a byte.

• A killobyte (KB) is 1024 bytes. The size of a data file is often measured in killobyte.

• A megabyte (MB) is often used to measure the storage capacity of a disk or the amount of main memary. The totall size of a collection of files within a folder may be messured in megabyte. A megabyte is 1048576 bytes. 1 MB is about as much data as 500 pages of double spaced text.

• A gigabyte (GB) is equivalent to 1024 MB. The memary capacity of a many larger storage devices such as hard drive is messured in gigabytes. 

• A terabyte (TB) is equivalent to 1024 GB.

Analogue and Digital data

Computer system work with Digital data. In a digital system every unit of information is reduce to a combinations of bits. Each bit can have one of two valuves: ON or Off.


Many data transmission media use analogue transmitions. An analogue transmition uses variatoin in a signal wave to represent data. When someone speak to you, you hear a sound wave and interpret the data as word depending on the variations in tone and pitch.


Therefor many computer device include componnents to convert data between analogue and digital formats. For a example  a high point of wave might represent On the low point Off. Example of componnents that convert between analogue and digital include the sound adapter and a computer modem.

Sound input and output

Sound card and speaker
Many computers especially home computers are equipped with speakers. Speakers take the signal genarated by a sound card and convert it into sound.
If your computer has speakers you can listen to music CD's or hear sound effects genarated by software. This capability is often used by educational softwares and computer games.

Speech Synthesiser

A speech synthasiser receied a output of a computer and turn it into speech played throught the speaker.
A microphone can be attached to a sound card provide audio input with suitable software a microphone can also be used to issue commands and create files.

Visual output devices

output device display information from the computer to the user. the main output devices display data on a screen print data on paper, and play data as sound.
With modern software the screen display is the most important interface the user has with a computer. All commands are issued using a mouse or keyboard to select elements of a graphical user interface such as menues and toolbar.

Displaying data on screen requires two components.

• The graphic card is often connected to an expansion slot (PCI or AGP) on the motherboard. Many graphic cards are optimised to display 3D graphics effects. They often incorporated sophisticated. microprocessor and have thrir memory so that the screen display can be kept updated as smoothly as possible.
• The visual display unit displays an image on a screeen recording to the data supplied to it by the graphic card.

These componnents need to be compatible in order to work together. Almost all modern display system use the SVGA standerd. SVGA support high colour depth resolution and refresh rate. Older display standerd include VGA and XGA which are not compatible of such high performance.

The Central Processing unit

The central processing unit (CPU)is the part of the computer that processes and calculates data. You can think of the CPU as the ''brain'' of the computer.

• The CPU is an advance microprocessor. A microprocessor perform calculations on data and determins what to do with the result of those calculations.
• The CPU is sent instructions by the computer's software. The CPU processes many millions of instructions per second and passes the resultto other components of the computer. The speed at which the CPU works is the main factor influencing the performance of the computer.
• To process an instructions, the CPU retrives data from storage . Data that is required urgently by the CPU is usually store in memory storage. Data that need to be retained when the computer is switched off is held in disk storage. When the CPU has complete the instructions, the data is written back to storage and the CPU moves on the next instructions. Following on some instructions, The CPU update other componnents.

Components of a Microcomputer

computers are made up of many components. Most of these are internal. However, some are connected externally, using ports. A port is a kind of plug, usually located at the back of the computer.

Components located outside the computer's case are reffered to as peripheral devices.

Because they use components, PC's are customisable. You can add components for specific task, such as playing sound, and choose more powerful and expensive part to make a high-end pc.Conversely, you can specify less powerful, cheaper components for a basic offer computer.
This means that pc's veryquite widely in terms of performance, cost and the sort of applications that they can run.

What is a computer

A computer is a device that manipulates data according to a sets of instructions. Nearly all computers are based on the use of electronic circuit ,although a computer does not have to be electronic.

Three elements required for a computer to perform useful task hardware, software and the computer's user.

The piece of equipment that make up a computer system are called hardware. Many parts are contain with in the computer's case. Other parts are connected to the computer.These allow information's to be entered and retrieved.

The instructions that a computer follows come from software. Operating systems, spreadsheet programs and payroll programme are example of software.Software means that the same hardware can be put to a variety of use.

Software provides an interface for the user to control the computer system. The user create data files by typing data and selecting commands from the interface.

Undestanding the Basic concepts of IT

An Information technology (IT) system is one that processes,stores, and/ or transfers information. Information can take many different form: word, numbers, pictures, sound or video.

AN IT system could use computers, the telecommunications network, and other programmebele electronic devices. ( In fact, because of the importanceof communication in IT, the term ICT.
[Informations and communications technology] is often used in preference to IT).

• Because it involves many different and often highly specialist areas, IT is often seen as a very daunting subject. However, the basis of IT is simply to help us to improve the way we deal with information in all areas of our lives.
• IT is used in business, industry, government, education, and helthcare. It is also an important part of everyday home and social life.
• Computers enable us to process  information and perform specific task much more quickly than we could do ourselves.
• IT systems are very flexible and can be made to prform a variaty of different tasks.
• IT networks, such as the global internet, allow us to distribute and share informations very quickly.