Higher%20Computing%20Computer%20Systems

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Higher Computing Computer Systems

• Computer Software

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What is an operating system

• The operating system is a program that controls
  the entire operation of the computer and devices
  which are attached to it
• Most of the OS is permanently stored on hard disk
  and loaded in to RAM when the computer is on

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The bootstrap loader

• When the computer is switched on the initial part
  of the OS is loaded from chip (ROM)
• The bootstrap loaders function is to load the
  rest of the OS from disk

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The single user operating system

• A SUOS is only capable of being used by one
  person at a time
• The main functions of a SUOS are
• Interpreting users commands (CLI)
• File management
• Memory management
• I/O management
• Managing processes
• Resource allocation

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The Command Language Interpreter

• The CLI is the layer with which the user
  interacts in order to give instructions to the
  computer it interprets user commands

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File management

• The FMS is concerned with the efficient use of
  the computers backing storage devices and media
• The FMS holds the details of where each file (or
  part of) is held on the disk
• The FMS is also known as the Disk Operating System

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Memory management

• The MMS controls where programs and data are
  placed in main memory
• The MMS keeps track of the total amount of main
  memory available and which programs and data are
  currently loaded

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Input/Output management

• The I/OMS communicates directly with the
  peripheral devices
• The I/OMS handles the transfer of data between
  the peripherals and the processor

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Process management the kernel

• The kernel is the part of the OS which is
  responsible for managing interrupts
• e.g. from the printer
• The kernel is responsible for managing processes
• from the CLI e.g. copy. A process initiated by
  the CLI may result in an interrupt

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Resource allocation

• RS is the way of managing which resource is
  available for use at any one time by a process
• Efficient RS ensures that the processor is kept
  busy, by maintaining a queue of processes that
  are always ready for the processor
• A scheduler prioritises the queue

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The OS working - an example

• Loading the file myfile from disk
• Using the CLI you issue the command to open a
  folder
• The kernel interrupts the current CLI process and
  passes the request to the FMS
• The FMS requests the I/O system to read the
  disks catalog track and loads a list of file
  names
• The CLI allows the user to choose the filename
  myfile from the list
• The FMS passes the physical location of the file
  to the I/O system
• The I/O system loads the file from disk and hands
  it over to the MMS
• The MMS places the file in the main memory and
  you again have control of the computer

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Utility programs

• UPs can be part of the OS or a separate program
• Virus checker
• Disc editor
• Defragmenter
• Backup
• Emulators
• Converters, compressors and expanders
• Email and web filters

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Virus checker

• A virus checker is a utility program which is
  designed to check a computer system for viruses
• A virus checker will then remove the virus
• Virus checkers have to be kept up to date in
  order to be effective against new viruses

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Disc editor

• A disc editor allows the user to edit data
  directly on the surface of a disk
• DE programs incorporate automatic disk repair and
  data recovery functions
• Newer hard drives smart drives have their own
  software for which monitors the performance of
  the drive

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Defragmenter

• Files are often split and saved on different
  parts of a disk
• This increases the time taken to access the file
• A defragmenter gathers all the free space on the
  disk together and reunites all the fragmented
  files that can be accommodated

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Before defragmenting
After defragmenting








Used block
unused block
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Backup

• Backup software can help to automate the process
  of making regular backups
• Backup software can allow you to synchronise
  files between two devices or media
• When two copies of the same file exist on
  different media the newer copy will replace the
  older version

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Emulators

• An emulator is a program that allows one type of
  computer to behave as if it was a completely
  different type
• A computer running emulator software will run
  much slower than the computer it is emulating
• Virtual PC allows apple computers to emulate
  Windows OS computers

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Converters, compressors and expanders

• Converters change the format of a data file from
  one application type to another
• Compressors reduce the size of a data file
• Expanders decompress a compressed data file

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Printer drivers

• A program that takes the codes in the document
  and translates them into the appropriate code for
  the printer in use

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Email and web filters

• An email filter is software that monitors emails
  which are sent on a network
• The Regulation of Investigatory Powers Act (2000)
  gives employers the right to monitor employees
  email
• A web filter monitors URLs and the content of web
  pages be accessed by the user

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File formats

• Standard file formats have been developed to ease
  the transfer of data between software developed
  by different manufacturers e.g. text files - RTF
• Each type of application software has its own set
  of standard file formats e.g. JPEG used in
  photographic manipulation software

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File formats - GIF

• Graphics Interchange Format
• For low resolution bit-map colour graphics
• 256 colours possible
• Compressed files
• Fast to load and transfer via internet
• Interlacing allowed
• Animations also possible
• GIF uses lossless compression

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File formats JPEG, MPEG

• Joint Photographic Experts Group
• Standard for still picture compression
• 16.7 million colours
• Uses lossy compression
• Typically achieves 10 to 1 compression with
  little perceivable loss in image quality
• Motion Pictures Expert Group
• Standard for moving pictures

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File formats - TIFF

• Tag(ged) Image File Format
• For high resolution bit-map images
• Large files unsuitable for WWW
• Uncompressed
• Used by DTP, book and magazine printing

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Matching software to tasks (1)

• Production of a multimedia catalogue
• Multimedia authoring package e.g. Macromedia
  Director
• Additional software for editing individual
  elements
• Video
• Audio
• Graphic
• Text
• And
• CD or DVD writing software

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Matching software to tasks (2)

• Setting up a LAN in a school
• Modern OS capable of peer to peer networking
• Client server needs network OS software
• Database servers need specific software e.g.
  Microsoft SQL
• Database application such as Filemaker Pro are
  available in single or network versions

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Matching software to tasks (3)

• Development of a school website
• Web page creation software with WYSIWYG page
  editing
• Additional software for editing individual
  elements
• Video
• Audio
• Graphic
• Text
• And
• Testing using a range of browser software

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Software compatibility issues

• Software that works on a computer system is said
  to be compatible
• Issues that can affect the compatibility of the
  software are
• Memory requirements
• Storage requirements
• OS compatibility

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Memory requirements (RAM)

• If a system cannot meet the minimum RAM
  requirements to run the software the software
  will not run
• If there is insufficient RAM to hold the complete
  program then part of it will be stored on disk,
  virtual memory
• Running programs using VM will slow the program

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Storage requirements

• Full installation - The amount of backing storage
  needed to hold the complete program after
  installation (and decompression)
• Minimal installation The least amount of
  storage requirement needed to run the program,
  normally the installation CD is still needed to
  run the program

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OS compatibility

• Three main OS used on desktops and laptops
• Windows
• Unix
• Apple OS
• Users need the correct version of software for
  the different OS
• Windows OS not always backward compatible

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Viruses

• A virus is a program which can destroy or cause
  damage to data stored on a computer system
• A virus infects host files and is distributed
  along with them

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Worm

• A worm is a virus that can make copies of itself
  and spread between computers without having to be
  attached to a file

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Trojan horses

• A Trojan horse is disguised as another type of
  file

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What viruses infect

• A virus may infect different parts of the
  computer system
• File viruses
• Boot sector viruses
• Macro viruses

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File viruses

• File viruses attach themselves to files
• They add malicious code into the files
• Typical files that are infected are Windows OS
  files with .COM and .EXE extensions

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Boot sector viruses

• All magnetic disks contain a boot sector
• The boot code can become infected with a virus
  and is loaded when the machine is rebooted
• Less common now that floppy discs are no longer
  in popular use

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Macro viruses

• A macro virus infects documents e.g. spreadsheets
  or word processing documents
• A macro virus causes a malicious series of events
  once the document is opened
• The macro virus will also infect any new
  documents created by the same application

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Virus code actions

• Virus act differently according to how they are
  programmed
• The action the virus may carry out when run
  include
• Replication
• Camouflage
• Watching
• Delivery

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Replication

• A worm can make copies of itself this is known as
  replication

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Camouflage

• Mixed in with good code
• Malicious or false code is changed every time it
  runs to avoid detection
• Disguise the code so that it looks harmless
• All these techniques are used to avoid detection
  by anti-virus programs

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Watching

• Sleeper virus lays in wait for a particular sign
  which will activate it
• A date or time or action
• Time bomb (triggered by a date)
• Logic bomb (triggered by an action)

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Delivery

• The method used by the virus to enter the system
• Shared backing storage devices
• Connected to the internet
• Web pages
• Downloads
• Emails
• Email attachments

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Anti-virus detection

• Anti-virus software detection techniques include
• Use of checksum
• Searching for virus signature
• Heuristic detection
• Memory resident monitoring

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Use of checksum (1)

• A checksum is a value calculated for a given set
  of data
• The answer to the calculation is the checksum
• It is used to check that data has been
  transmitted and received correctly

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Use of checksum (2)

• The checksum is transmitted along with the data
• The receiving computer performs the same
  calculation and checks the sum
• If they are the same its ok
• If the dont match the anti-virus software will
  issue a virus warning

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Searching for virus signature

• Anti-virus programs can find viruses inside
  programs by scanning them for virus signatures
• A virus signature is a characteristic pattern in
  a file
• These files can then be disinfected
• Polymorphic viruses modify their code to avoid
  virus signature detection

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Heuristic detection

• Detect viruses a heuristic or rule of thumb
  method
• Imprecise method although useful
• If it looks like a virus and behaves like a virus
  then its probably a virus
• Used to detect new viruses

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Memory resident monitoring

• Anti-virus software that loads in to the
  computers memory on start up
• Monitors all programs and data loaded in to the
  computers memory
• Can slow down the processing speed of a computer
  as everything is checked for viruses

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The End