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2.7 Nature of Hardware

2.7 Nature of Hardware. In this section you must be able to describe: Broad characteristics Capabilities Limitations Of current: Input and output devices Storage devices Communication devices Processing devices And describe relevant contexts for their use. An ICT System.

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2.7 Nature of Hardware

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  1. 2.7 Nature of Hardware In this section you must be able to describe: • Broad characteristics • Capabilities • Limitations Of current: • Input and output devices • Storage devices • Communication devices • Processing devices And describe relevant contexts for their use

  2. An ICT System • In general terms, ICT systems take an input, and process it to produce an output. Process Input Output

  3. Input Devices We looked at these in detail in section 2.1: • Manual input – mouse, tablet, handwriting recognition • Input from paper – OMR, scanners and OCR, magnetic ink, barcodes, punched cards • Voice recognition – command and dictation • Alternative input methods – magnetic stripes, barcodes, fingerprint scanners, etc. And the benefits and drawbacks of each.

  4. Processors • Processors are usually described by the manufacturer and model, e.g. Intel Pentium, or AMD Athlon - and a clock speed, e.g. Intel Pentium 4 2.8GHz. The clock speed is measure in Hertz, with the symbol Hz. • If a processor had a clock speed of 1 Hz, it would mean that it completed one instruction per second. It might take several of these instructions to do something useful. • Processors get quite hot and need a cooling device consisting of a heat sink (a series of fins to radiate the heat) and a fan

  5. Storage • Non-volatile, usually magnetic media - stored without power • Slower - access time of around 8ms • Cheaper, e.g. 40Gb for £35 Primary storage (e.g. RAM): • Volatile - i.e. contents are lost without power • Fast - access time of around 7ns for PC RAM • Relatively expensive - 1Gb DDR RAM costs £60 Secondary storage (e.g. hard disc):

  6. Sector Disc Storage Constant angular velocity Constant linear velocity • CLV discs (e.g. Compact Discs) slow down as sectors nearer the edge are read - the sectors are the same physical length so that capacity is increased

  7. Storage Media Most storage media are either optical or magnetic, e.g.: • Hard disc • Floppy disc • CD-ROM / CD-R / CD-RW • DVD-RAM / DVD-R / DVD-RW • DAT, AIT and other tape formats • Zip drives • Solid state storage – e.g. SD, XD, CompactFlash

  8. Storage Media Access can be: • Random – any file can be accessed in any order • Serial – files must be accessed in order they were saved – e.g. with a tape And media can be: • Read-only • WORM (Write Once, Read Many times), e.g. CD-R • Readable and writable (e.g. CD-RW)

  9. A A A B A B B B B B Storing Files on a Disc • File A is written • File B is written • File A is edited • Disc is fragmented • The disc is now defragmented - the sectors are contiguous and so quicker to read • Location of file is stored in the File Allocation Table (FAT) A

  10. Output Devices There seems to be less variety in output devices: • Printers • Plotters • VDUs • Speakers and other audio devices • Computer controlled devices – e.g. for cutting or embroidery They require: • Some sort of connection (e.g. cable) to the computer • A driver to translate instructions into codes that the device can understand

  11. Visual Display Units The key properties of computer displays are: • Resolution – the number of pixels it can display • Size – measure diagonally, usually in inches • Technology – CRT, LCD, Plasma, TFT, etc. • Refresh rate – how many times per second does it flicker? • Response time – how quickly can the display be updated? • Contrast ratio (usually only given for flat panel monitors) • Colour depth – how many colours can they display?

  12. Choosing a Printer Factors to consider when choosing a printer: • Volume of output – does it need to be fast? • Print quality – resolution or dpi (dots per inch) • Location – are there environmental considerations? • Colour – is it necessary • Different sizes of paper, envelopes and transparencies • Cost – both the initial cost and the cost of consumables • Noise (i.e. whether you need it to be quiet)

  13. Printer Technologies • Impact Printers – those that strike the paper • Dot matrix • Daisy wheel • These are used when carbon copies are required • Non-impact printers • Ink-jet / Bubble-jet • Laser Printer • Dye sublimation (photo) printers • These are quieter but cannot be used with carbon paper

  14. Communicating with I/O Devices Peripheral devices can be connected via: • Parallel connections • Serial connections They are often slower than the PCs and can also use: • Buffering – temporary storage in RAM • Spooling – temporary storage on disc To queue the data going to or from a device

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