More Input Devices

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More Input Devices

• Microphone
• A device that converts sound waves into audio
  signals.
• These audio signals can then be converted into
  digital values and stored in the computer.
• Microphones are often used with webcams for video
  conferencing.

2
More Output Devices

• Liquid Crystal Display (LCD)
• Liquid Crystal Display. The type of display found
  on digital watches, lap-top computers and some
  flat-screen monitors. Their major advantage is
  low power consumption, leading to long battery
  life for portable devices.
• TFT
• Abbreviation of thin film transistor, a type of
  LCD flat-panel display screen where each pixel is
  controlled by its own transistor. This technology
  provides the best resolution of all the
  flat-panel techniques. Also sometimes called
  active-matrix LCDs.

3
More Output Devices

• Loudspeakers
• Loudspeakers are audio output devices which take
  the output from a computers soundcard and covert
  it back into audio waves.
• Loudspeakers can be anything from small
  headphones to surround-sound cinema style
  speakers.

4
More Backing Storage

• CD-R
• recordable compact disk. Disk can be written to
  by a user with the proper kind of CD drive.
  Cannot be erased to be written on again. One time
  write only!
• CD-RW
• similar in virtually all respects to a CD-R,
  except that a CD-RW disc can be written and
  erased many times. This makes them best suited to
  many backup tasks. CD-RW drives can also create
  CD-R discs.
• DVD-R
• A write-once, recordable format. DVD-R drives can
  write DVD-R discs, which can be written only
  once.
• DVD-RW
• DVD-RW (recordable/rewritable) drives can write
  both DVD-R discs and DVD-RW rewritable discs,
  which can be written to and erased many times.

5
More Backing Storage

• USB Flash Drive
• Universal Serial Bus is an interface which allows
  various devices to be attached to a computer.
• A flash drive is a device which contains memory
  chips which can be used to store data
  permanently.
• These devices are small and portable. They have
  capacities up to 2Gb (the most common being 512
  Mb (0.5 Gb).

6
Comparison of printers in terms of

• Speed (ppm)
• Pages per minute is used as a means of comparing
  printers. General the more pages a printer can
  print in a minute the better for the user (the
  user has less time to wait for the printouts).
• Capital Costs
• The initial cost of the printer and its
  installation are capital costs. Printers can
  range in price from a few tens of pounds to
  thousands or tens of thousands of pounds.
• Some printers require network cabling, special
  power supplies, additional computers etc. All of
  this adds to the capital cost of the printer.

7
Comparison of printers in terms of

• Running costs
• The running costs are the costs to operate the
  printer. These include the cost of
• Paper and other printing media
• Power
• Ink or toner for the printer
• Service contacts or support for hardware failure
• Resolution
• Is an indication of the sharpness of images on a
  printout. It is based on the number and density
  of the dots used. The more dots used in an image,
  the more detail can be seen and the higher the
  image's resolution.
• Resolution for printers is measured in dots per
  inch (dpi). The higher the dpi the better
  quality the image.

8
Comparison of backing storage

• Speed (data transfer)
• Backing storage devices can be compared in terms
  of the time it takes to transfer data from the
  disc to the computer.
• Speeds are most commonly measured in Mbits
  (megabits i.e. thousands of bits per second)
• A typical floppy disc drive transfers data at 1
  Mbits/sec
• A typical 32x CD-ROM drive transfers data at 4.8
  Mbits/sec
• A typical 16x DVD-ROM drive transfers data at
  16.7 Mbits/sec
• A typical Hard disc drive transfers data at 150
  Mbits/sec
• These are all typical statistics and given as a
  rough guide
• Cost
• Floppy drives are cheaper than CD-ROM drives
  which are cheap than DVD-ROM which are cheaper
  than Hard-discs
• All devices can be compared on a cost basis.

9
Comparison of backing storage

• Capacity
• Refers to how much data a medium can store.
• Floppy disc is 1.44 Megabytes
• Most common USB Flash Drive size is 512 Megabytes
• CD-ROM is 673 Megabytes
• DVD-ROM is a maximum of 17 Gigabytes
• The most common hard disc size if currently 120
  Gigabytes

10
OS - Different modes of processing

• Interactive systems with background job
  capability
• Some operating systems allow a background process
  to occur at the same time as a foreground
  interactive process.
• The foreground process is the one that accepts
  input from the keyboard, mouse, or other input
  device. Background processes cannot accept
  interactive input from a user, but they can
  access data stored on a disk and write data to
  the video display unit.

• For example, some word processors print files in
  the background, enabling you to continue editing
  while files are being printed.

11
Hierarchical filing system

• A filing system in which directories have files
  and subdirectories beneath them
• A hierarchical filing system is one that uses
  directories to organise files into a tree
  structure.
• Directories (folders) can store more folders
  and/or files.

A Hierarchical Filing Structure
12
Types of Access

• There are two types of access
• Random Access (also called Direct Access) devices
  retrieve the data you want straight away e.g.
  CD-ROM drive, Hard disc drive, floppy disc drive.
• Sequential (also called Serial) devices have to
  move through all the data, record after record,
  to find the data you need e.g. Cassette tape,
  magnetic tape.

13
Types of access

• Sequential Access
• To go from file A to file Z in a
  sequential-access system, you must pass through
  all intervening files.
• Sequential access is sometimes called serial
  access.
• Random Access
• Refers to the ability to access data at random.
  In a random-access system, you can jump directly
  to file Z. Disks are random access media, whereas
  tapes are sequential access media.

14
Device Drivers

• Computer operating systems are written by
  software companies e.g. Apple, Microsoft etc.
• It is impossible for these companies to know
  about every single item of hardware that has been
  or might be developed for their operating system.
• To get round this problem the manufacturer of an
  item of hardware writes a small program called a
  device driver for their device. This program
  includes instructions for the operating system
  about how to communicate with the hardware
  device.
• A device driver is software that controls how a
  computer communicates with a device, such as a
  printer. For example, a printer driver translates
  information from the operating system into
  information the printer can understand.

15
The Operating System

• The operating system (OS) is the most important
  program used by the computer.
• The OS in most modern computers is stored on hard
  disc and is loaded into RAM when the computer
  starts up.
• Some computers store their OS in ROM (e.g. some
  palmtop computers) so that it cannot be erased by
  accident. ROM operating systems load very
  quickly.
• The operating system controls and monitors the
  operation of the computer system.
• The filing system is part of the OS and it
  controls the loading and saving of programs and
  data from backing storage.

16
Modern Operating Systems

• Examples of operating systems which are disc
  based
• Windows XP for the PC
• System X for Apple Macintosh
• Linux for large fileservers and networks.
• Examples of operating systems which are ROM based
• JavaOS for Network Computers (NCs)
• PalmOS or Windows Mobile for palm top and
  handheld devices (computers, phones, MP3 players
  etc.).

17
Standard Functions of the OS.

• User interface
• the OS provides the means of communicating with
  the computer system (Icons, commands etc. are all
  provided by the operating system).
• Manages memory
• The way that memory is allocated to programs is
  controlled by the OS.
• Controls input/output
• The access to all devices attached to the
  computer is controlled by the OS. For example,
  the OS can stop two programs trying to use the
  same device at the same time.

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More OS - Standard Functions

• Filing System
• The filing system manages backing storage
• The access to all types of backing storage
  devices is controlled by a special part of the
  operating system called the filing system.
• The filing system will prevent two programs
  trying to access the same files at the same time.
• Error Reporting
• When an error occurs the operating system
  provides information to the user about what has
  happened and, sometimes, how it can be fixed.

19
Resource allocation

• When a computer is running the demands on the
  systems resources (i.e. memory, input/output
  devices, backing storage etc.) may be greater
  than the resources available. To deal with this
  a resource allocation system is built into the
  OS.
• Various techniques are used to prevent two
  programs demanding the same resource at the same
  time (e.g. two programs can't both send files to
  the printer at the same time).
• The resource allocation system also ensures that
  all programs running on the system receive as
  much processing time as possible.

20
More about the Processor

• The processor is made up of three main parts.
• The CONTROL UNIT fetches program instructions
  from the memory storage locations, decodes and
  then executes them.
• The ALU (Arithmetic/Logic Unit) carries out all
  the calculations as instructed by the control
  unit.
• The registers are small storage locations inside
  the processor where data can be stored while the
  processor is executing instructions.

21
Word

• All processors have a maximum number of bits
  which they can process in one operation.
• This number of bits determines the word size of
  the computer.
• An X-Box is a 32-bit computer system because it
  can process 32 bits in one operation, hence its
  word size is 32 bits.
• The old ZX Spectrum (a computer popular in the
  early 1980s) had a word size of 8 bits.
• The next generation of Play Station (PS3) will be
  64-bit, a 64 bit word size.

22
Calculation of image storage

• A black and white graphic uses 1 bit to stored
  each pixel (picture element).
• If the image is 300 pixels by 200 pixels then it
  is stored using a total of 300 x 200 bits i.e.
  60000 bits.
• Divide this by 8 to give the number of bytes
• 60000/8 7500
• Divide this by 1024 to give the number of
  kilobytes
• 7500/1024 7.324
• Round up to ensure you have enough storage
• 7.324 7.33 Kb

23
Types of translator

• There are two types of translator for high level
  languages.
• Compiler
• A program that translates source code into
  machine code. The compiler gets its name from the
  way it works, looking at all of the source code
  and collecting, reorganising and converting the
  instructions into machine code.
• Compilers require some time to create an
  executable program. However, programs produced by
  compilers run much faster than the same programs
  executed by an interpreter.
• The program produced by the compiler is
  executable. It does not need the compiler or the
  source code.
• Many compilers are available for the same
  language. For example, there is a FORTRAN
  compiler for PCs and another for Apple Macintosh
  computers. This makes the program source code
  PORTABLE (able to run on a number of different
  computer processors).

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Types of translator

• Interpreter
• An interpreter translates high-level instructions
  into a machine code line by line. Each HLL
  statement is converted, in turn, into machine
  code and then executed.
• An interpreter can immediately execute high-level
  programs (unlike a compiler). For this reason,
  interpreters are sometimes used during the
  development of a program, when a programmer wants
  to add small sections at a time and test them
  quickly. Also interpreters are often used in
  education because they allow students to program
  interactively.
• The advantage of an interpreter over a compiler
  is that it does not need to go through the
  compilation stage during which machine code
  instructions are generated.
• Many interpreters are available for the same
  language. For example, there is a BASIC
  interpreter for PCs and another for Apple
  Macintosh computers. This makes the program
  source code PORTABLE.

25
Portability of software

• All programs must be translated into machine code
  in order to run.
• Different types of processors use different types
  of machine code.
• Translator programs (compilers and interpreters)
  are written for specific processor types.
• The same source code (the name given to the file
  containing the HLL program) can be sometimes be
  translated by more than one translator and
  therefore run on more than one type of computer.

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Portability of software

• 10. Print Hello
• 20. Let a 20
• 30. For x 1 to a
• Print x
• 50. Next x
• 60.
• 70..
• 80.

Source code
Compiler for Processor 1
Compiler for Processor 2
The same source code can be translated by two
different programs to run on two different
processors. This means that the source code is
portable
Processor 1
Processor 2
27
More on Input Devices

• Voice Recognition
• With voice recognition systems the computer can
  understand the words spoken to it and can carry
  out commands associated with the words. Using
  voice recognition a letter can be dictated
  instead of being typed at the keyboard.
• Handwriting Recognition
• Handwriting can be recognised and the computer
  can convert the written text into typed text for
  storing.

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More on Output Devices

• Voice Output
• Voice output from a computer system is also know
  as speech synthesis. Some voice output programs
  are know as text readers. They take a text file
  and recite it to the user.

Other speech synthesis programs can tell the user
what they are doing (for example floor
announcements in a speaking elevator).
Hello, I am Hal!
29
Input devices for disabled users

• A wide range of input devices can be used to
  allow people with a range of disabilities
  operating computer hardware and software.

• joystick and switch
• combinations enable an individual lacking
  sufficient mobility to use a full keyboard to
  access a computer through an on-screen keyboard
  or other "virtual" substitute
• keyboard alternatives
• allow individuals unable to use a standard
  keyboard to input keystrokes with a mouse,
  headmount, or other specialized device.

30
Output devices for disabled users

• screen magnifiers
• enlarge the information displayed on the computer
  screen in a range of magnifications and a variety
  of fonts.
• screen readers
• are intended primarily to assist individuals who
  are blind or otherwise visually impaired. These
  solutions include magnification software, screen
  reading programs, and Braille translation
  devices. Screen readers, or screen review
  programs, are highly specialised applications
  that will read, sometimes with the help of a
  speech synthesizer, what is currently displayed
  on the screen. Other packages are specialized to
  read scanned documents, essentially turning the
  computer into a reading machine for printed
  documents.