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 In general terms, ICT systems take an input, and process it to produce an output. Process InputOutput

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.

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

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

Disc Storage Constant angular velocity Constant linear velocity Sector 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

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

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)

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 A A B B A B B A B B

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

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?

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)

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

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