ICT2 - Information: Management and Manipulation
Output Devices
Criteria for Choosing a Printer
Volume of Output (fast durable printer required for high volumes)
Print Quality (high quality print required for business letters and reports)
Noise (in a busy office, a noisy printer can cause problems)
Multiple Copies (carbon copies can only be produced by some types of printer)
Colour (is required by some but not by others)
Cost (cost of printer and running costs are an issue)
Dot Matrix Printers
This is an impact printer, which produces print by striking the paper through a ribbon. 24 pin dot matrix printers produce better quality than 9 pin because the dots are closer together.
NLQ - Near Letter Quality (this is produced by printing each line twice, so that the spaces between the dots are filled in)
Cost - very cheap to run
Quality - poor
Colour - can be achieved with coloured ribbons but the quality is poor
Noise - can be very noisy, even when in a case
Multiple Copies - can print through carbon paper
Volume - dot matrix printers are slow, so they are not suitable for high volume
Inkjet Printers
They work by firing droplets of ink at the page.
Cost - cheap to buy but expensive to run
Quality - good but varies according to the paper used, Copies can smear
when wet.
Colour - good quality
Noise - fairly quiet
Multiple Copies - cannot print through carbon paper
Volume - Faster than dot-matrix printers but still not fast enough for high
volume printing. Not cost effective either.
Laser Printers
Toner (powdered ink) is transferred to the page and fused onto the page by heat and pressure.
Cost - More expensive than inkjet printers but some black laser
printers are now under £500. Toner cartridges are about £60 but they
last for around 5,000 copies
Quality - Very good, even on cheap photocopying paper
Colour - Colour laser printers are very expensive
Noise - quiet
Multiple Copies - cannot print through carbon paper
Volume - Quick for high volumes
Plotters
They produce high quality line drawings, such as building plans and electrical circuits.
Vector Plotters - use pens to draw images using point-to-point data. These are relatively low in price.
Raster Plotters - More expensive. They don't use pens. They produce very high density drawings.
VDU
Visual Display Unit (otherwise known as monitors)
Resolution - determined by the number of pixels used to represent a full screen image (e.g. 640x480, 800x600)
Colour - Colours displayed depend on how many bits are used to represent each pixel (e.g. 256, 65k, 16m)
Size - Standard size for a desktop PC is 14". Higher resolutions are suitable for wider screens.
In Windows, the display properties in the control panel can be used to adjust the resolution and colour level. Some resolutions and colour options may not be availeble. This will depend on the quality of the graphics card and the capabilities of the VDU.
Communicating with the CPU
Buses transfer signals between the various components of the computer. They are simply wires that connect various pieces of hardware
Internal Bus - connects the components of the CPU
External Bus - connects the CPU to the memory and to the input/output units.
Each input/output device is connected to the bus via an interface unit.
Parallel and Serial Data Transmission
Parallel transmission is generally used for the connection of peripherals such as printers and scanners, whilst serial transmission is often used for communication within large-scale networks.
Serial transmission: All data is transmitted along a single line/cable one bit after another.
Parallel: Data is spread across several wires and transmitted simultaneously (several bits side-by-side).
Parallel transmission is only suitable across short distances. Therefore, it is often used for printers of scanners. The shorter the cable, the faster the data transmission.
Parallel transmission is now old technology. Most printers and scanners are now USB (universal Serial Bus) devices, which are generally faster than parallel devices.
Buffering
A buffer is an area of memory used for holding data during input or output transfers. For example, the CPU processes data much faster than a printer can print. Therefore, input and output are handled independently of the main processor, leaving the CPU free for other tasks. Information that is to be printed is held in the buffer. The amount that can be held in the buffer depends on the amount of printer memory.
Spooling
This is a technique to speed up communication between devices which operate at different speeds. Output to a printer can, for example, be spooled to disk. When the printer becomes free, the output will be printed. Therefore, several users on a networkcan all use the same printer because each user's output is spooled to a different part of the disk.
Installing hardware devices such as a printer
Whenever a device is added, a device driver needs to be installed to control the device. The driver specifies information about the printer, including information about its features, control sequences, and so on. When an instruction is given to print, the driver translates information about text formatting etc. into a form that the printer understands.