• A computer is an information processing machine.

• A computer only follows the instructions it is given.

• Data is Input, Processed and then Output.

What is a Computer?

I’m ONLY a machine!

Hardware and Software

• Hardware refers to all the parts of the Computer System that we can touch.

Examples of hardware are monitors, joysticks, printers, processors etc.

• Software refers to all the programs and data that we use with the computer.

IPO - Input, Process, Output

INPUT PROCESS OUTPUT

Data is INPUT into the computer system

It is then PROCESSED to produce useful Information as OUTPUT.

Computer - Block Diagram• The Computer System consists of four

parts.

Input, Processor [CPU], Output, Backing Storage

Backing Storage Devices

Input Devices

Central Processing Unit (CPU)

Output Devices

MAIN MEMORY - ROM and RAM

• ROM is Read Only Memory• Data stored in ROM can only be read, it can never be

written over or deleted. We normally store important programs in ROM to do with the computers Operating System (see later). NON VOLATILE MEMORY

• RAM is Random Access Memory• It can be written to and read from. It is where most programs and data are stored while the computer is being used. RAM loses its contents when the computer is switched off. VOLATILE MEMORY

RAM ROM

PROCESSORData Flow

Hardware Devices• Devices are either INPUT, OUTPUT or

BACKING STORAGE.

• Input devices allow us to enter data into the computer system (mouse, microphone etc).

• Output devices allow us to receive information from the computer system (monitor, speakers, robot).

• Backing storage devices allow us to store programs and data so that we can use them later (floppy disc, magnetic tape, CD-ROM).

Types of Input

• KeyboardMost keyboards are of the QWERTY type but not always. They have always been used for inputting data to the computer

• MouseThe mouse is very important in WIMP systems and is used to move a pointer around the screen and make selections by pressing a button

Advanced types of Input

• TrackballA trackball is basically an upside down mouse. A trackball allows the user to move a small ball in order to move the pointer across the screen.

• Graphics TabletA graphics tablet allows the user to draw on a special worktop. As the user draws the details are stored on the computer system. These devices are most often used by architects and designers.

JoystickThe main use of a joystick is to play computer games by controlling the way that something moves on the screen.

• Joysticks can be used to control movement from side-to-side, up-and-down and diagonally.

• A joystick will also always have at least one button on it which can be used to make something happen like making a character in a game jump or a gun fire.

Touch ScreenA touch screen can detect exactly

where, on its surface it has been touched.

Touch screens are used in a lot of fast food chains and restaurants because they are easy to keep clean and re-program if changes need to be made to the menu.

Digital Camera• A digital camera can store many more pictures than an ordinary camera.• Pictures taken using a digital camera are stored inside its memory and can be transferred to a computer by connecting the camera to it.

• A digital camera takes pictures by converting the light passing through the lens at the front into a digital image.

Scanner• A scanner can be used to input pictures and text into a computer.• There are two main types of scanner; Hand-held and Flat-bed.

• Voice Recognition With voice recognition systems the computer can understand the words spoken to it and can carry out commands associated with the words. Using voice recognition a letter can be dictated instead of being typed at the keyboard.

• Handwriting RecognitionHandwriting can be recognised and the computer can convert the written text into typed text for storing.

Optical Character Recognition• OCR

Is used to convert paper typed documents into text files that can be edited and stored on a computer system.

OCR software can search a scanned image for the shapes of letters, numbers etc. When it finds shapes that match it converts them to the correct text and stores them in a file.

Example of OCR device : Scanner

Magnetic Ink Character Recognition (MICR)

• Magnetic Ink Character Recognition, or MICR, is a character recognition technology used primarily by the banking industry to facilitate the processing of cheques. The technology allows computers to read information (such as account numbers) off of printed documents

• MICR characters are printed in special typefaces with a magnetic ink or toner

• As a machine decodes the MICR text, it first magnetizes the characters in the plane of the paper. Then the characters are passed over a MICR read head, a device similar to the playback head of a tape recorder

Example of OCR : Bank Cheque Printed No.

Optical Mark Recognition (OMR)• Optical Mark Recognition (also called

Optical Mark Reading and OMR) is the process of capturing human-marked data from document forms such as surveys and tests

• Many traditional OMR (Optical Mark Recognition) devices work with a dedicated scanner device that shines a beam of light onto the form paper. The contrasting reflectivity at predetermined positions on a page is then utilized to detect the marked areas because they reflect less light than the blank areas of the paper.

Example of OMR : objective type question test

Types of Output

• VDU or MonitorVisual Display Unit (VDU) is the proper name for the computer monitor. The VDU allows us to see the output from the computer.

• PlotterA plotter is a device used for creating a hard copy of the output from a computer system. Plotters use special pens to draw the output as a

series of lines. Plotters are often used to output building drawings and designs.

Monitor - Visual Display Unit

• The quality of the output on a monitor depends on its resolution.

• The resolution of a monitor depends on the number of pixels that it can display.

• A monitor or VDU is an output device that can display graphics and text and video.

• The picture on a monitor is made up of thousands of tiny coloured dots called pixels.

More on Output Devices.• There are three types of printers

– laser – inkjet– dot-matrix

• Printers are used to create a hard copy of output from the computer system (normally on paper).

Laser printers are expensive,

produce high quality printouts, can produce 8 to 12 pages in a minute

and are almost silent when they are working.

More on Output Devices• Inkjet printers are cheaper than laser printers,

they produce reasonable quality printouts (not quite as good as laser), can also printout in colour, can print 2 to 5 pages in minute but there are a little noisy.

• Dot-matrix printers are the cheapest, they produce poor quality printouts, some can print in colour, they struggle to print 1 page in a minute and they are VERY noisy.

• Backing storage is used to store programs and data when they are not being used or when a computer is switched off.

• When programs and data are needed they are copied into main memory but also still remain on backing storage.

• Magnetic tape drives, floppy disk drives and hard disk drives are all examples of backing storage devices.

• WORM - Write Once Read ManyA WORM is a writable optical disc. An optical disc is any disc that can be read using light (normally laser light). WORM drives use a high powered laser to burn the data into the disc. This can then be read in the same way that CD-ROM's are read. Because the data is burnt onto the disc each disc can only be written once and the data written is permanent.

Magnetic tape, floppy disc, hard disc and CD-ROM are all types of

backing storage.

Backing Storage Devices

• A floppy disc can be used to save data.

• It can also be used to make a backup

copy of small files.

• A backup is a second copy of your data that you take in case something happens to the original.

• You should always make a backup of important files.

Write Protect TabDisc Label

The Floppy Disk

• Size : 3.5 inch• Capacity : 1.44 Mb

The Hard Disc and Drive• A hard disk is a circular metal disk coated with magnetic material and usually sealed in a hard disk drive inside the computer.

• Some hard disk drives are not permanently fixed inside the computer but are removable.

• Data stored on a hard disk can be accessed much more quickly than data stored on a floppy disk.

• Hard disks can store much more data than a floppy disk. A typical hard disk inside a personal computer can hold many gigabytes of data.

The Hard Disc and Drive

• Hard discs are normally built into the computer.

• In a modern home PC the hard disc would typically store 10Gb of data or more.

Non-magnetic storage

• Non-magnetic storage involves the use of media not coated in magnetic material.

• Examples of this are: CD-ROM, Video Disc, Digital Video Disc (DVD) and WORM.

• These use pits and bumps (lands) on the disc to store digital data and use laser light to write and read them.

Capacity• The size of memory, hard disc space, floppy drive

space, programs, data files etc. are all measured by the number of bytes, kilobytes, megabytes or gigabytes (1024 megabytes) of data they

contain.

445 floppy discs

=1 CD-ROM

Types of Access

• There are two types of access

• Random Access (also called Direct Access) devices retrieve the data you want straight away e.g. CD-ROM drive, Hard disc drive, floppy disc drive.

• Sequential (also called Serial) devices have to move through all the data, record after record, to find the data you need e.g. Cassette tape, magnetic tape.

Types of access

• Sequential Access• To go from file A to file Z in a

sequential-access system, you must pass through all intervening files.

• Sequential access is sometimes called serial access.

• Random Access• Refers to the ability to access data at

random. In a random-access system, you can jump directly to file Z.

Types of Media

• Media is the material used in devices.

• Examples of media are Floppy disc and CD-ROM.

• If CD-ROM is the MEDIA then the CD-ROM drive is the DEVICE.

Multimedia

• Multimedia systems combine graphics, text, sound, video and animation to provide a rich experience for the user.

• Many interactive multimedia software titles are available now.

• Often these are stored on CD-ROM e.g. Microsoft Encarta.

Virtual Reality

• Virtual Reality involves the user entering a 3D world generated by the computer.

• To be immersed in a 3D VR world requires special hardware e.g.

• A headset (containing goggles, headphones and a position tracker)

• A data glove or data suit so that the users body can interact with the VR world.

It consists of at least one input device, a processor and one output device.

A standalone computer system is a computer system that is NOT connected to other computers.

A computer system is a collection of parts that work together.

What is a Computer System ?

Monitor-

Output

Printer-

OutputCentral Processing Unit

Mouse-

Input

Keyboard-

Input

A Computer System ?

• A network is made up of two or more computers linked together.

Advantages are:* Share devices between computers* Share data between computers* Share programs between computers* Saves time

Computer Networks

Types of Networks

There are 3 types of computer network: • A local area network (LAN) – computers

are linked from office to office, or building to building.

• A metropolitan area network (MAN) – not a WAN but may link computers in different parts of a city, not a LAN but may link computers from building to building.

• A wide area network (WAN) – computers are linked city to city, or country to country.

• A local area network is a computer network across one building or site.

Fileserver

Printer

Work Station

Network Cable

A Typical Local Area Network (LAN)

• link computers in different parts of a city, not a LAN but may link computers from building to building

Metropolitan Area Network (MAN)

Wide Area Network• A wide area network is normally used to link groups of

computers across long distances.

• A multinational company in New York will have its own LAN,

but to link with its Japanese offices LAN, it will need to make

use of a WAN.

• The WAN will be made up of telephone lines, radio and

satellite links, all run by the local public providers. These will

have their own charges.

• Alternatively the company may pay for a permanent link

between offices, known as a leased line. The company pays a

fixed rate for the permanently open connection.

Topology• Topology is the way devices are linked

in a certain design either physically and / or logically.

• There are different topologies:– Bus;– Ring; – Star;– Mesh.

• There are different types of network:– Peer to Peer;– Client Server.

Bus Network

Terminal Central Cable

Workstations, File Server, Printer.

• Data is sent from the sender to all other devices (nodes), this may be the server or a workstation.• There is no computer in control but there may be a server that stores the data files.• Advantages: simple, reliable, cheap, short cabling.• Disadvantage: slow when busy or a large network, as only one computer at a time can transmit data.

Bus Network

What would happen to the network if a workstation

breaks down?

X

Ring Network• Data is sent from the

sender, it goes around the

ring being read by each

computer, if it is not for

that one, it gets sent to the

next, until it reaches its

destination.

• Data has to wait its turn

before sending, special

software (token) writes an

address for sender and

destination.

Workstationswith In and Out

Connections.File server and

Printer.

Token Ring

Ring NetworkWhat would happen to the network if a workstation

breaks down? XAdvantage: all nodes can access the Token equally, high speed.

Disadvantage: all on one path, therefore maintenance is high

for faults and failures.

Star NetworkData is controlled by

a central server,

messages sent and

received are read by

the controller.

Each workstation has

Its own dedicated link.

Advantages: fast with

high volumes of data,

extra nodes added without

any disconnections.

Central Controller

Node

Workstations

Star NetworkWhat would happen to the network if a workstation

breaks down?

XDisadvantages: if the

Central controller fails thewhole system is down, large amounts of cableare required, so it may

get expensive.

Mesh Network

Data sent from node to node goes by a direct link.

Possible to leave out some paths as there aremany alternative routes.

Advantages: very fast, and fault tolerant.

Disadvantages: very largeamounts of cabling, resultingIn higher maintenance costs.

Mesh Network

What would happen to the network if a

workstation breaks down?

X