Computer Systems

Computer Systems

A computer system is made up of two parts: andSoftware Hardware

Hardware Hardware is the physical parts of a computer system.

Hardware for a computer system consists of: • Central Processing Unit • Main Memory • Input devices • Output devices • Backing storage

Block Diagram for a Computer System

Central Processing Unit (CPU) This is where all the sorting, searching, calculating and decision making is done. CPUs are usually single chip microprocessors.

Main Memory • Main memory is made up of two types of memory chip. • RANDOM ACCESS MEMORY – RAM • READ ONLY MEMORY – ROM

Random Access Memory RANDOM ACCESS MEMORY – RAM – this is read/write memory and is used to store the current program and data. It is the user memory. The contents of RAM is lost when power is switched off – it is VOLATILE.

Read Only Memory READ ONLY MEMORY – ROM – is used to store programs and data permanently. Its contents can only be read and cannot be added to or altered.

Input Devices These allow a user to enter data into a computer.

Keyboard This permits a user to type text, enter numbers etc. A keyboard has all the keys of a normal typewriter plus a few extra ones that are used for special tasks like delete and page up.

Touch Sensitive Screen Atouch sensitive screen uses invisible infrared signals and detectors around the edge of a screen. When the screen is touched, the person’s finger will ‘break’ the infrared beam.

Graphics Tablet This is a flat pressure-sensitive board with a pen or pointer connected to it. Using one, a person can draw a shape in the same ways as he/she would with pencil and paper.

Mouse As most computer systems have moved to a WIMP environment, this has become very common. A mouse is used to open and close windows, select icons, bring up menus and move a pointer on the screen.

Trackball A trackball or tracker ball is a bit like an upside-down mouse. The device has a ball on top as well as a number of buttons. The user operates it by moving his/her hand over the ball.

Joystick This is used in games and controls the pointer on the screen by the user moving a stick.Other types include steering wheels (with accelerator and brake pedals!) and a game controller.

Lightpen Light pens can be used to ‘draw’ on the computer screen. the pen contains a light sensor which can detect the point of light that is used to create the picture on the screen.

Scanner A scanner is used to input a photo, picture, drawing or text on paper into a computer. It uses reflected light to detect the image. Scanners are also used to read barcodes on items in a shop etc.

Digital Camera A photograph taken by a digital camera can be downloaded to a computer and viewed on screen. The photograph can be edited, printed on a colour printer and saved on hard disc. The camera doesn’t use film but captures the image on a CCD (a light sensitive memory chip) and stores the pictures on a memory card.

Web Cam This type of camera is used to capture video pictures. These can then be transmitted live between computers.

Voice Recognition Voice recognition allows speech to be input into a computer system. The user speaks into a microphone. In some systems, for example paying bills on the telephone, the user is required to say which option from a given list is needed.

Handwriting Recognition Some computers can read the users writing and turn it into print. The user writes on a pressure sensitive tablet connected to a computer system.

OutputDevices These get processed data out of the computer

Plotters • A plotter is a computer printing device for printing of vector graphics. • Plotters have usually been used in computer aided design for plans and large drawings. • Pen plotters print by moving a pen or other instrument across the surface of a piece of paper. Flatbed plotter Drum plotter

Headphones Speakers Sound Output Sound Output are devices that produce sound from a cable connected from the computer to either speakers or headphones.

Printers • Laser • Expensive to buy • Cheap to run • Very fast • Very good quality • Inkjet • Cheap to buy • Expensive to run • Good quality • Slow

Projectors • Projectors project what is on the monitor • They would project onto a white screen or a wall • This lets a lot of people see what’s on the monitor at the same time Prices • The cheapest projector is from NEC and is £219. • The most expensive one is £33039 Panasonic.

Backing Storage

Magnetic Storage Hard and floppy Disks Block – track 3 sector 1 Sector tracks

Magnetic Storage - Disks • Disk surfaces coated with iron coating • Particles can be magnetised to point North(1) or South(0) • When a file is saved the operating system makes a note of the filename and which track/sector block it is saved to • File can be found again by direct (random) access– going straight to the block

Magnetic Tape • Used for Backup • Sequential (Serial) Access • Must read through all earlier files to find one File 6 File 5 File 4 File 3 File 2 File 1

Optical Storage Aluminium Layer Pit Land Land Sensor Laser Sensor Laser Sensor Laser 0 1 1

Optical Storage • CD –ROM – data burned when disk made • CD-R – data can be burned (ie saved)once • Use for archiving • CD-RW – data can be written (ie saved) as often as required • DVD-ROM – data burned when disk made • DVD-R – data can be burned (ie saved)once • Use for archiving • DVD-RW – data can be written (ie saved) as often as required

Flash Memory • USB pen drives • Camera cards • No moving parts • Fast direct access • Small and portable • Currently up to 16Gb

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Computer Systems