A Level IT

1
A Level IT

• Output Devices

Chapter 28
2
Printers

• Come in all shapes and sizes. Type of printer
  chosen will depend on
• volume of output
• quality of print required
• location of printer
• requirement for multiple copies
• requirements for colour

3
Types of printer

• Dot matrix

• Laser

• Ink jet

4
Dot matrix

• Impact printer, print head with 9 - 24 pins
  strikes paper through ribbon
• Near letter quality (NLQ) by printing line
  twice, but takes twice as long to print.
• Many are bi-directional.
• Versatile, most can print in condensed, standard
  and enlarged mode, in bold or normal print,
  some graphics
• Noisy

5
Ink jet

• Non-impact printer, fires ink droplets at the
  page
• Compact, quiet, cheap and high resolution but
  slow
• Large coloured areas can get wet, buckle, and
  smear
• Colour ink cartridges very expensive

6
Laser

• Toner (powdered ink) fused to page by heat and
  pressure
• Increasingly popular, price falling
• Output of very high quality at up to ten pages
  per minute
• Virtually silent in operation
• Toner cartridge expensive but lasts 5,000 copies

7
Plotters

• Produce high quality line drawings such as
  Building plans or electronic circuits.
• Pen (vector plotters)

• or
• Penless (raster plotters)

8
Visual display unit (VDU)

• Three basic attributes size, colour and
  resolution.
• It has its own fixed amount of RAM associated
  with it to store the image being displayed on the
  screen
• The amount of RAM will determine the resolution
  and the maximum number of colours for display.
  Note that
• The resolution is determined by the number of
  pixels (addressable picture elements) used to
  represent a full-screen image
• The number of colours that can be displayed is
  determined by how many bits are used to represent
  each pixel.

9
Communicating with the CPU

• Data, addresses and control signals transferred
  by buses
• Two types
• Internal buses within CPU
• External buses between CPU and I/O
• Need interface to convert signals and deal with
  difference in speed.

10
Parallel Serial Data Transmission

• Data may by transferred in either parallel or
  serial mode
• Parallel 1 byte at a time over shorter
  distances
• Serial 1 bit at a time over longer distances
• Printers usually use parallel but now also use a
  new type of interface. USB.
• Universal Serial Bus Find out about USB. What
  is it? How does it work? Speed? Etc.

11
Buffering

• Buffer is an area of memory used to hold data
  during I/O procedures
• Used because the speed of CPU and printer are
  different.
• Which is quickest?
• Buffer holds data for printing thus allowing the
  processor to get on with other tasks.

12
Spooling

• Spooling is a technique used to further speed up
  the printing process and release the CPU.
• Items are saved to disk (high speed device) and
  then printed from disk.
• Used on networks
• Uses a queuing system.

13
Installing hardware devices

• When you add a new device such as a printer,
  scanner, mouse, soundcard or videodisk player to
  a computer system, you have to install a piece of
  software called a device driver to control the
  device.

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Installing

• A printer-driver file is a piece of software that
  specifies information about the printer,
  including details about
• printer features
• descriptions of fonts (sizes and styles)
• control sequences that the printer uses to
  produce various formats, accents etc.
• When you give an instruction to print, the driver
  translates the information about fonts,
  formatting, highlighting etc. into a form that
  the printer can understand.

15
Installing

• When you attach a new printer to a computer, you
  have to do the following before you can print
  anything
• Install the printer-driver file for the printer
• Select the port you want to assign the printer to

16
Tasks

• Q 1, 2 4 New Book page 156/157
• Q 1, 2 Old Book Plus
• When installing or configuring a particular WP
  package, the documentation states that the
  correct printer driver must also be installed.
  What is a printer driver and why is it necessary?