Identify the constituent parts of a total computer system.

Identify the constituent parts of a total computer system:

Hardware – input and output units

Backup storage; central processing unit;

Software – applications package;

Operating system;

The main function of a computer system is to process data. When data has been processed and output it becomes information. The main stages of this procedure are:

The Input Stage - where data is put into the computer.
The Processing Stage - where the data is processed.
The Output Stage - where the results are displayed.

A computer also needs to store data for later use. This is done on a backing storage device.

Hardware – input and output units

INPUT DEVICES

Barcode reader
Barcodes are different groups of vertical bars that can be read by an optical scanner. Barcodes are printed on nearly every product that you can buy. Shops use barcodes because they are cheap to produce and very durable.

Concept keyboard
A concept keyboard is a flat board that contains a grid of buttons. Each button can be programmed to follow instructions. An overlay sheet is placed on the grid with an explanation for each button. They are used in primary schools with young children. Many modern fast food restaurants have overlays with either a description or picture of the meals that are available to make ordering easier.

Digital camera
A digital camera allows you to take pictures and to store a digital photographic image that can be read by a computer. You can then transfer the images directly from your camera on to your computer. Digital cameras are often used by estate agents for producing advertising and sales material.

Graphics tablet
A graphics tablet consists of a flat pad (the tablet) on which the user draws with a special pen. As the user draws on the pad the image is created on the screen. Using a graphics tablet a designer can produce very accurate on-screen drawings.

MICR (Magnetic Ink Character Reader)
Magnetic ink characters are the strange looking numbers that appear at the bottom of cheques. These characters are used because they are very difficult to forge or damage. Banks use MICR to read the numbers from the bottom of cheques to obtain data such as account numbers and bank sort codes.

Magnetic strip
Magnetic strips are built into many plastic cards such as cheque guarantee cards, cash-point cards and personal identity cards. The magnetic strip on the back of the card can hold the personal details of the card owner and, with the necessary PIN, will allow access to secure information e.g. bank account details.

MIDI (Musical Instrument Digital Interface)
A MIDI system allows you to attach a musical instrument to your computer, for example a musical keyboard. You can then store a musical sequence on a computer and then have the computer play it back to you.

OMR (Optical Mark Reader)
An optical mark reader reads marks made by pencil on a printed form into the computer. OMR systems are suited to reading pre-printed forms and check-boxes such as National Lottery number selection sheets and multiple-choice exam papers.

Scanner
Scanners are now a cheap and common way of getting images into a computer. They can also be used with OCR (Optical Character Recognition) software to scan in text.

Touch screen
A touch screen is a special type of VDU, which has a grid of light beams or fine wires criss-crossing the screen. When the screen is touched (usually to choose an on-screen option), the computer senses where you have pressed. Due to the vast amount of information they can store, touch screen operated computers are generally used in the provision of public information and are found in places such as airports.

Video digitiser
A video digitiser takes an image from a video camera or television and converts it so that it can be used by, and stored on, a computer. Video sequences captured using a video digitiser are often used in multimedia presentations.

Voice recognition (microphone)
A microphone is used with a voice recognition system. This can be used with a word processing program to enter text. It can also be used as part of security systems - only certain digitally stored voices have access.

Other input devices

Joystick
Light pen
Mouse
QWERTY keyboard
Sensors
Tracker ball

OUTPUT DEVICES

Monitors or Visual Display Units (VDUs)
Monitors or VDUs are the most common output device and include desktop monitors and Liquid Crystal Displays (LCDs).

Printers

Laser printers produce a very high quality output, are very quiet and very fast although quite expensive to buy.
Ink-jet printers are cheaper to buy, offering black and white or colour printing with reduced levels of quality and speed.
Dot-matrix printers are not so common today. They are comparatively noisy ...

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Joystick
Light pen
Mouse
QWERTY keyboard
Sensors
Tracker ball

OUTPUT DEVICES

Monitors or Visual Display Units (VDUs)
Monitors or VDUs are the most common output device and include desktop monitors and Liquid Crystal Displays (LCDs).

Printers

Laser printers produce a very high quality output, are very quiet and very fast although quite expensive to buy.
Ink-jet printers are cheaper to buy, offering black and white or colour printing with reduced levels of quality and speed.
Dot-matrix printers are not so common today. They are comparatively noisy and low quality but are cheap to run and ideal for draft copies.

Plotters
A plotter can be used to produce high quality, accurate, A3 size or bigger drawings. They are usually used for Computer Aided Design (CAD) and Computer Aided Manufacture (CAM) applications such as printing out plans for houses or car parts.

Other devices

Speakers
LCD projectors

BACKUP STORAGE

Backing store - magnetic disks

Magnetic disks are the most common backing storage medium. Magnetic disks include 3.5-inch portable floppy disks and also the hard disk drive fixed inside your computer.

Floppy disks
You can read data from and write data on to a floppy disk. Floppy disks can be moved between computers and usually store up to 1.44 Mb. They have three main uses:

to transfer small files of data from one machine to another
to back up important small files that are stored on your hard disk
to store restricted files that you don't want all other users of your computer seeing

Hard disks or hard drives
Hard disks have storage capacities thousands of times larger than floppy disks. Data can be transferred to and from a hard disk much more quickly than from a floppy disk.

Your hard disk will be where you store:

the operating system
programs
the majority of your data files

Backing store - optical disks

CD-ROM (Compact Disk Read Only Memory) disks are optical disks that use the same technology as musical compact disks. They store up to 650 Mb of data and a laser beam is used to read the data off the disk.

Data is written onto the CD-ROM disk before it is sold and cannot be changed by the user. As CD-ROMs are much bigger than floppy disks, they can be used for multimedia applications such as encyclopaedias and can store pictures, sounds and video clips.

It is now possible to record on to CDs with a CD writer.

Backing store - magnetic tape

Magnetic tapes or cartridges are principally used for backup. As they are small, robust and portable, with the ability to store far more than a floppy disk, they are often used to back up important documents and files from the hard-drive. Magnetic media is also used for long term storage and the archiving of data.

CENTRAL PROCESSING UNIT

CPU stands for Central Processing Unit. It is the ‘brain’ of the computer. In fact, it is a microprocessor (chip) fixed to a circuit board inside the computer.

There are three main parts of the CPU -

1. The A.L.U. (Arithmetic and Logic Unit), which does all the arithmetic and logical operations.

2. The Main Store Memory. This is where data and programs are stored.

3. The Control Unit. This is the part, which controls the sequence of all computer operations.

Arithmetic Logic unit is the part of the computer where all calculating and testing happens. Data is sent to and received from the the ALU by the control unit.

Computer memory can be divided into two main types, main store and backing store. Main store consists of a large number of electronic circuits and all data and information that is processed by the computer has to go through main store.

When a sequence of instructions (program) is being executed by the computer system the control unit ensures that the data that is used within the computer is collected and sent from the peripherals and the special registers (special areas of RAM). As long as the data is controlled as it travels around the computer system the computer works ok. If the data is not controlled or sequenced correctly then the computer will crash.

Software – Applications Package

A computer system is made up of hardware and software. The hardware is the physical components like input, output and backing store devices. Software is the computer program that instructs the computer to perform particular operations.

Software consists of very simple instructions that tell the computer what to do with the data that it is processing. These instructions are carried out so quickly the computer seems to be doing complicated things.

The computer user will have bought the computer system to perform one or more tasks. The software that makes the computer perform these user-related tasks is called applications software.

Some applications software may be written to perform a particular specialised task, such as stock control or payroll for particular company. Other applications such as a word processor program or spreadsheet may be general purpose or generic. Generic software can be used in a variety of ways for different purposes. A word processor program could be used to produce posters, prepare legal documents or write a school assignment.

Nearly all applications programs can be customised. This allows the user to set up the application in a way that suits them. Examples of customisation include setting up special dictionaries for a word processor, choosing the format for currency or dates and setting default fonts and background colours.

Software needs to be customisable because it will usually be used by a large number of users each having different needs. If the software can be customised then the user can configure it to in a way that allows them to work efficiently. For this reason generic packages such as word processors, spreadsheets and databases usually include a large number of configuration options. A non-generic application, written for one specific purpose, will normally have fewer configuration options because there will be a more limited user base and the tasks that the users will carry out are more clearly defined.

Sometimes a customer's software needs cannot be met by an existing package. In this case software may be specially written for the customer. This is called bespoke software and the customer should end up with an application that exactly matches his or her needs. However software development costs are high so this is an expensive option. In addition it can take a months or even years for software to be developed. Once the software has been produced it is likely to have a number of bugs that will need to be sorted out.

OPERATING SYSTEMS ON A MICROCOMPUTER

An operating system is a program that controls and organises the general operation of the computer. A computer cannot work without an operating system. Remember, without an operating system you cannot use your computer.

On a microcomputer an operating system will:

deal with the transfer of programs in and out of memory
allow the user to save files to a backing store
control the transfer of data to peripherals such as printers
provide the interface between user and computer e.g. Windows 98, Acorn RISC OS
issue simple error messages

THE OPERATING SYSTEM ON LARGER COMPUTERS IS VERY DIFFERENT, THOUGH MANY OF THE JOBS ARE SIMILAR IN PRINCIPLE.

Larger computers such as mainframes operate differently from the simple PC. They can process two or more programs at the same time and may have to deal with many users at the same time. This sort of operation requires very complex operating systems.

Some general features of operating systems are:

they control the backing store and peripherals such as disk units and printers
they control the loading and running of programs
they organise the use of memory between programs
they organise processing time between programs and users
they organise priorities between program and users
they maintain security and access rights of users
they deal with errors and user instructions

MODES OF OPERATION

Computers can operate in many different ways requiring different and complex operating systems.

Real time processing
A real time system responds to incoming data immediately. Computers that run in real time have to be very fast and have a lot of processing power.
Computers operating in real time are often dedicated to the control of systems such as industrial processes, planes and space flights. The computer has to react immediately to input data by issuing output signals to the systems being controlled.

Other examples of real time processing are holiday and travel booking systems.

Multiprogramming
Multiprogramming is a method of operating such that several programs appear to be running at once. The term usually applies to mainframe operation when the computer is switching between a number of different programs or dealing with a number of different users.

The jobs are usually given priorities. The operating system switches jobs in and out of processor time according to priority. For example, while one job is being allocated printer time, another will be being processed in memory. The processor is so fast that it seems that many jobs are being processed at the same time.

Multitasking
Multitasking usually applies to microcomputers whereby the computer is running a number of applications apparently at the same time.

Multi-access or multi-user
A multi-access (or multi-user) system is one where a number of users work with terminals on-line to a central computer. The central processor deals with users in turn; clearly the more users, the slower the response time. Generally, however, the processor is so fast that the response time at the most is a fraction of a second and the user feels they are being dealt with immediately.

Batch processing
A batch processing system is where programs or data are collected together in a batch and processed in one go. Typically the processing of payrolls, electricity bills, invoices and daily transactions are dealt with this way.

This method of operation lends itself to jobs with similar inputs, processing and outputs where no human intervention is needed. Jobs are stored in a queue until the computer is ready to deal with them. Often batch processed jobs are done overnight.