St Roch’s Secondary School

Standard Grade Computing

Systems Booklet

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St Roch’s Secondary School

COMPUTER HARDWARE

Computer hardware can be described as the physical parts of the computers system – the bits we can see and touch. The bits inside and outside the computer that make it work!

A single piece of hardware is known as Device.

The following is a simplified diagram of a computer system. The arrows show the way that information flows around the computer system.

In the diagram above information flows to the CPU from an Input Device and to the Output Device from the CPU.

Information can flow to and from the Central Processing Unit from Memory and Backing Store.

In the next few pages we are going to find out what part each of the above parts of the computer take within our computer system!

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CENTRAL PROCESSING UNIT

Other names for the CPU are the Microprocessor or just processor. This is the brain of the computer system – it does all the sorting, searching, calculating and decision making.

In lots of computers today all the processes are carried out by a single chip. A chip is a specially treated piece of silicon and is very small – only a few millimetres in size.The CPU is divided into three parts:

CONTROL UNIT / Controls the order in which instructions are carried out.
ARITHMETIC AND LOGIC UNIT / performs all the calculations (e.g. ADD, SUBTRACT etc) and Logical operations (e.g. AND OR etc)
REGISTERS / Are temporary storage locations within the processor. Registers are used to hold the programs and data while they are being processed.

MEMORY

Memory is a set of chips which store programs and data. There are two types of memory: ROM and RAM.

ROM MEMORY (READ ONLY MEMORY)

Read only memory is permanent memory. When the computer is switched off programs are still permanently stored inside the ROM chip. Because it is read only memory you cannot write the memory. This means that to change the information you will have to replace the chip with a new one.

Advantages of having programs stored in ROM are:

  • Programs are instantly available when the computer is switched on.

  • No programs are accidentally lost or altered.

  • The program is not lost when the computer is switched off.

Disadvantages of having programs stored in ROM are:

  • The program cannot be changed or updated.

RAM MEMORY (RANDOM ACCESS MEMORY)

Random Access Memory is temporary memory. When the computer is switched off, the contents of the RAM chips are lost. RAM memory can both be read from and written to, this makes it ideal for storing data and programs which the computer is currently using e.g. a game or a word processing program.

The advantage of storing a program in RAM is:

  • The program cannot be saved permanently and is lost when the computer is switched off.

EFFECTS OF CHANGES IN TECHNOLOGY

Each year, the number of storage locations and circuits (connections) that can be placed on a single chip get bigger. This has affected computer systems because:

  • The price of memory chips is continuing to go down.

  • The memory size of computers (ROM and RAM) has gone up.

  • Chips work faster and can handle more data in a single operation.

  • Complete computers can be produced on a single chip.

  • Computers are now much smaller.

There is a constant demand for faster and more powerful computers due to the advances in more complex computer programs

INPUT DEVICES

An input device is a device which allows data to be entered into a computer system. We will look at each input device in detail later in the booklet. Here is a list of possible input devices:

Foundation / General/Foundation / Credit/General/Foundation
Keyboard / Scanner / Sound Card
Graphics Tablet / Microphone / Specialised Input Devices for Disabled Users and Virtual Reality
Touch Sensitive Screen / Digital Still Camera / Input Devices for Multimedia
Mouse / Digital Video Camera
Trackball / Web Cam
Trackpad
Joystick

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OUTPUT DEVICES

An output device is device which allows data to be displayed or passed out a computer system. We will look at each output device in detail later in the booklet. Here is a list of possible output devices:

Foundation / General/Foundation / Credit/General/Foundation
Printers – Laser and Inkjet / Liquid Crystal Display Monitor (LCD) / Sound Card
Plotter / Thin Film Transistor Monitor (TFT) / Graphics Card
Monitor / Specialised Output Devices for Disabled Users and Virtual Reality
VDU / Output Devices for Multimedia

BACKING STORAGE

Backing Storage is used to permanently store programs and data. Computers need backing storage because data in RAM is lost when the computer is switched off.

DIRECT/RANDOM ACCESS AND SEQENTIAL ACCESS

DIRECT/RANDOM ACCESS / SEQUENTIAL ACCESS
In random or direct access you can go straight to the file you wish without having to go through all the others. Just like you can when you want to locate a track from your audio CD. / In sequential access you have to go through all the files in order they were written to get to the one you wish to access. Just like you have to when you want to locate a track from a tape – you have to fast forward through it to you find the one you want.

STORAGE CAPACITY OF BACKING STORAGE

The capacity of backing storage is the quantity of data that can be held in a particular medium. Here is the storage capacity of most types of backing storage at a glance:

BACKING STORAGE MEDIUM / TYPICAL CAPACITY / TYPE OF ACCESS
Magnetic Tape / 20 to 100 gigabytes / Sequential
Floppy Disk / 1.44 megabytes / Direct
Hard Disk / 20 to 500 gigabytes / Direct
CD-ROM, CD-R, CD-RW / 650 or 700 megabytes / Direct
DVD-ROM, DVD-R, DVD-RW / 4.7 to 17 gigabytes / Direct
USB Flash ROM / 16 megabytes to 8 gigabytes / Direct

TYPES OF COMPUTER SYSTEM

MAINFRAME COMPUTER

A mainframe computer is a computer system with:

  • Very powerful processors
  • Lots of backing storage
  • Large Internal Memory

Mainframes are designed to process large volumes of data at high speed. They are used by large business such as banks and mail order companies etc.

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DESKTOP COMPUTER

A desktop computer is the most common type of PC. This type of computer is designed to sit permanently on a desk – not easily carried around. It is a collection of different hardware devices.

The most common components of a desktop computer are:

  • Processor and Main Memory
  • Monitor
  • Keyboard
  • Mouse
  • Hard Disk
  • CD/DVD Drive
  • Speakers

LAPTOP/NOTEBOOK COMPUTERS

A laptop computer is so called because it possible to be used on your lap – they are lightweight and easily carried round. However, nowadays they are more commonly called Notebook Computers. It has built in peripherals e.g. LCD screen and a trackpad instead of a mouse. It has just as much memory and backing storage capability as a desktop computer but can work from batteries as well as mains power.

PALMTOP COMPUTER (PERSONAL DIGITAL ASSISTANT)

A Palmtop (sometimes known as a Personal Digital Assistant) is a computer which will fit in the palm of your hand and is very easy to carry round. Because of its size it cannot use the normal input devices – so instead uses a stylus (bit like a pen that can be used on a computer screen) and a touch sensitive screen (so that it can receive the input from the stylus). It has less processing power, memory and backing storage than any other type of computer.

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INPUT AND OUTPUT DEVICES

INPUT DEVICES

KEYBOARD

Keyboard is the input device most commonly used with computer systems. A keyboard is used for entering and text and numbers. The keyboard is normally arranged in the same way as a typewriter – the standard for the arrangement of the keys is called QWERTY. There are a few additions to this format – a numeric keypad at the side of the keyboard and functions keys to help with shortcuts.

MOUSE

A Mouse is used for pointing and selecting. Most Mouses have two buttons within it – one for selection and the other for menu options. Some often have a scroll button. A mouse is very important for Wimp systems when you have to select from menus and click on icons.

TRACKBALL

This works exactly the same way as a mouse, except that the ball is on top. The user rolls the ball around with the hand to operate it, and can select objects by pressing a button at the side of the device. Nowadays used most commonly in games arcade machines.

TRACKPAD

A Trackpad is a touch sensitive plate. It is used to control the movement of the pointer on the screen just like a mouse. It is most commonly used on Laptop Computers because like a trackball you don’t need to have extra space on your desk to operate it or have a flat surface

JOYSTICK

A joystick is an input device mostly used in computer games to control the way a picture on the screen moves. Joysticks have one or more buttons which can be controlled to perform specific actions. Often two joysticks are hooked up to the computer (games console) so that two users can place the game at once.

GRAPHICS TABLET

A Graphics Tablet is a flat pressure-sensitive board with a pen or pointer connected to it. By pressing on the graphics tablet with the pen, the pen’s position is sent to a computer – allowing very precise drawing (more than a mouse). A Graphics Tablet is most commonly used by graphic designers and architects and is used in CAD Applications (Computer Aided Design). A graphics tablet is also used with handwriting recognition.

With Handwriting Recognition the user hand-writes information – for the computer to store the shapes of the letters which can be used later for comparison. The user writes on a graphics tablet then the software compares the shape of the letters to the ones it has previously learned. Graphics Tablets used in handwriting recognition are often handheld.

TOUCH SENSITIVE SCREEN

On a touch sensitive screen looks like an ordinary monitor except the screen surface is pressure sensitive. Options are selected by easily by simply touching the screen. Touch sensitive screens are often seen in public places for tourist information and on games machines.

SCANNER

A scanner can be used to input printed drawings, photographs or text directly into the computer. A scanner works like a photocopier – a light is shone on the material and the scanner detects reflected light. You can use a Scanner for OCR (Optical Character Recognition) – software which scans text into a word processing package where it can be edited.

DIGITAL CAMERA (STILL CAMERA)

Digital Cameras is used for taking photographs and works just like an ordinary film camera, in that they both use a lens which focuses reflected light from the subject onto a sensor.

The difference is that on a film camera the images are stored and developed later. However, images within the digital camera can be viewed immediately on a small LCD screen – allowing the user to keep or discard. The images are saved on a memory card and can be downloaded on to your computer or printed. The larger the memory card the more images can be stored. However, in a digital camera it is possible to change the resolution of the image – the higher the resolution – the better the quality of the image it is and a higher storage capacity is required to store the image.

DIGITAL VIDEO CAMERA (CAMCORDER)

This is a device for taking movies. It works on the same principal as a digital still camera – but records the moving pictures to videotape instead of memory cards. The Digital Video Camera can be connected to a computer system in order to download the movie and edit it on the screen.

WEBCAM

A Webcam is a small digital camera, which is normally positioned on or beside a computer’s monitor in order to capture images which can be transmitted a cross a network. The video it takes is low in quality and the Webcam itself cannot store the video – the computer it is attached to does this. Webcams have made video conferencing possible.

Video Conferencing makes the use of a communications link and webcams in order to hold meetings across the Internet. It allows the users to see and hear each other .The advantage of this is that the users can be miles apart – therefore no time or money is spent having to attend meetings miles away.

MICROPHONE

A Microphone is used to allow sound to be input into a computer system. Most computers have microphones built in, usually above the screen or have an interface where a microphone can be plugged in. An external microphone will provide better quality recordings than internal microphone. A microphone is required for voice recognition.

In order to use Voice Recognition the computer system requires voice recognition software as well as the microphone. In order to use voice recognition you need to speak very slowly and clearly as the computer can only understand a few words. The user will usually have to teach the computer in order to recognise their voice by repeating words and phrases to it. Voice Recognition is of use to users who have difficulty using/seeing an ordinary keyboard.

OUTPUT DEVICES

MONTITORS

A monitor is an output device which accepts a signal from the computer and displays it on the screen. Some people call a VDU (Visual Display Unit) a monitor – however, a VDU is made up a monitor and a keyboard.

LIQUID CRYSTAL DISPLAY MONITORS (LCD)

These monitors are more lightweight and portable than their predecessors the CRT monitors (Cathode Ray Tube). In addition they use less power so therefore are ideal for use in laptops – they can work off battery as well as mains electricity. An LCD monitor consists of a thin layer of fluid sandwiched between two sheets of plastic, with complicated wiring used to apply electricity to different points changing the ability the ability of the liquid to transmit light. Therefore LCD is build up of light and dark dots (pixels) with each pixel varying in intensity. Therefore, each pixel can be switched on and off.

THIN FILM TRANSISTOR MONITORS (TFT)

TFT have the same advantages as LCD monitors but where as each pixel has to be turned on and off in a LCD monitor making it a slow process – leading to ghosting or smearing as the picture changes. TFT monitors avoid this problem by each pixel has a separate transistor to control each pixel, making it a faster process – therefore the display is improved. The disadvantage of TFT monitors.

Advantages of LCD and TFT Monitors over CRT Monitors / Advantages of CRT Monitors over LCD and TFT Monitors
  • Smaller and lighter so therefore more portable.
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  • Limited viewing angle.

  • Use less power than CRT monitors – therefore more energy efficient.
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  • Difficult to produce without defects, which makes them more expensive to produce

  • Do not flicker like CRT monitors or give out static electricity.
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  • Can cope with a wide range of resolutions – TFT/LCD monitors can’t

  • Do not suffer from a reduction in viewable size – CRT monitors do because of curved edges etc. (e.g. in 17 inch CRT monitor only about 15.8 inch is viewable).

PRINTERS

A printer is a device which is used to produce a printout or a hard copy of the output from the computer. Both laser and inkjet printers are able to produce black and white and colour images.

LASER PRINTER

Laser Printers use a special powder called toner to produce the image on paper. A laser beam is used to project the image of the page to be printed onto a cylinder known as a drum. The toner sticks to the parts of the drum which has the image on them. The paper is passed over the drum and image is transferred onto the paper.

INKJET PRINTER

These can produce high quality printouts of both graphics and text. They are particularly good at producing photographic printouts and can print on different surfaces even on CDs. An inkjet printout works by squirting small droplets of ink onto paper through tiny holes in the print head. The number of holes on the print head determine the resolution of the printer.

Here is a comparison of the two types of printer:

Laser Printer / Inkjet Printer
Speed / 12 ppm / 1-2 ppm
Capital Cost / Quite Expensive / Cheap
Running Cost / Cheap (mostly!) / Expensive for ink cartridges
Resolution / 1200 dpi / 2400 dpi
Quality / Good quality – no smearing as no wet ink. / Excellent resolution – possibility of smearing due to wet ink.

PLOTTER

A Plotter is another device used for making hard copies of output from the printer. The difference between a printer and a plotter is that a platter uses a pen to draw the computer output onto the paper. Plotters are very accurate and can produce drawing/plans on large scale dimensions (even larger than A4 and A3). They are often used in CAD and can be found being used by designers and architects.