Section Two The parts Of A Computer System

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Input Devices

An input device is any hardware which is used to enter data into the computer system.

QWERTY keyboards are the Most Common Input Device

1. QWERTY keyboards are the most common type of keyboards.

2. Each key is connected to a switch which closes when the key is pressed. This sends a signal to the CPU based on the characters ASCII code.

3. QWERTY keyboards are based on the way typewriters were designed.

4. A problem is that keying in can be slow unless the user has been trained or knows how to type.

Concept Keyboards are Faster but More Limited.

1. Concept keyboards are typically found in shops and restaurants. Each switch has a symbol or word on it, representing a piece of data (e.g) the price stored in the computer.

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Input Devices

A Joystick can Input Movement

1. These are mainly used to play computer games - but they can also be used to move a computer-controlled device such as a robot or a hospital body scanner.

2. The joystick is fixed to a base but can be moved in any direction.

Sensors convert the movement into coordinates, which tell the computer how to move the screen display or robot device.

Scanners Convert Images into Digital Data

1. A scanner works a bit like a fax machine. A picture is passed through the scanner and is converted into digital data - light and dark parts of the picture are given different codes. The computer then builds up a 'map' of the information based on thses individual 'bits' of data.

2. A problem is that these bitmap files can be very large and take up a lot of memory. A benifit is that the scanned image can be manupulated and edited easily and quickly.

3. Small scanners are usually hand-held. Larger flat-bed scanners fit onto a worktop.

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Other Input Devices

There are Eight More Input Devices

1. Digital Cameras are abit like scanners. They save an image as a series of dots called pixles. You can upload onto the computer and edit using photo-editing software. Benefits - film is not needed. Problem - high resolution imagines use lots of memory and currently use a lot of battery power.

2. Light Pens or Laser Scanners are used in supermarkets and libaries. They are used to read bar codes which contain data about the product. Benefits - it makes buying goods faster and reduces the chance of human error. Problem - the system is expenisve and depends upon the dat in the barcode and the computer system being accurate.

3. Video Digitisers convert analuge video pictures from a videotape or video camera into digital images which can then be manipulated using imaging software. This is called image grabbing. Benefit - Effect can be made that are impossible in real life. Problem - The cost.

4. Touch-Sensitive Screens are abit like concept keyboards - but instead of pressing a key, you touch the picture or word on the screen. Benefits - easy to use. Problem - More expensive than a keyboard and they get dirty from being touched.

5. Microphones are becoming increasingly used as an input device. They are used to input data into voice-recognition systems, which convert sound into text or commands for the computer. Benefit  - You can use dictation instead of having to type. Problem - The data uses a lot of energy.

6. Sensors are hardware that record environmental information and convert it to data. Examples include temperate sensors, light sensors and infra-red sensors used in burglar alarm systems.

7. Touch-Tone Telephones have a different tone for each button on the keypad. This sound is transmitted over the phone line and can be used to input commands into the system at the other end of the line. They are used by cinemas to run on-line box offices, by banks to do direct banking etc.

8. Midi Instruments - These instruments can be used to enter music into a computer package, e.g A keyboard can be played and the notes are recorded on the computer, where they can be edited. Benefits - the sound can be changed. Problem - the computer software is expensive.

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Page 12 - The CPU

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