2.7 Nature of HardwareIn 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.

ProcessInput Output

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

AB

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