computer science ocr

• advantages of a client server networkcentralised control

  • good security
  • One client computer crashing does not effect the other computers.
  • you can easily backup data and update software
• what does a fire wall do

  1. scans incoming and outgoing traffic
  2. compares to a criteria
  3. blocks traffic that’s unauthorised
  4. blocks incoming and outgoing traffic
• what does anti-malware do

  • identifies/scans for spy and malware
  • compares to a database of malware
  • alerts user to delete malware
  • or stops the download of malware
• what are four things that the router does

  • receives packets
  • sends packets to the correct nodes
  • assign IP addresses to nodes
  • converts from one protocol to another
  • determine the most suitable route for sending data.
• why does the number of devices affect the speed of a network

  • bandwidth is split between devices so..
  • less bandwidth for each device
  • if max bandwidth is reached devices can’t transmit data
  • central device has to handle more requests so may run slower
  • more collisions/higher error rate so more data needs to be re-transmitted
• name 4 types of utility software

  • defragmentation
  • backups
  • compression
  • encryption
• switch function


  A switch switches frames to the right node on a LAN using MAC adressing
• router function


  A router routes packets the the right LAN over a WAN using IP adressing
• how many bits in an IP address

  32
• how many bits in a mac address

  48
• what is clock speed measured in


  Hertz (1 GHz = 1 billion cycles per second)
• why do we have primary memory

  1. non-volatile so data is saved and won’t be lost when computer is turned off
  2. faster then secondary storage because it’s closer to CPU
• how to calculate the size of an image

  colour depth x resolution
• how to calculate the size of a sound file

  sample rate x duration x bit depth
• how many characters are in ASCII

  128
• how many does unicode use

  24
• why is unicode stored as hex numbers


  bc it takes up less space
• what is a bit map

  • image made up of different coloured pixels
  • each pixel has a unique binary number
• which compression reduces file size more

  lossy
• lossy compression

  • data is permanently deleted
  • reduces quality
  • cannot be used on text
• lossless compression

  • no data is lost
  • can be restored to original
  • less effective than lossy at reducing file size
• what does a device driver do

  • translates OS instructions into machine code
  • each peripheral need one built in
• what is multitasking 


  running multiple applications at once by giving each application a small time-slice of the processor time
• advantages of a peer to peer network

  • no specialist staff required
  • easy to maintain
  • doesn’t need exspensive hardware
  • can share files with peers easily
• disadvantages of a peer to peer network

  • worse security
  • can be hard to maintain well ordered storage
• advantages of client server networks 


  easier to..

  • manage
  • backup data
  • install software updates
• disadvantages of client server networks

  • can be exspensive
  • IT specialists requied to set up and run
• advantages of networks

  • users can share files
  • can share printers and stuff
  • servers can control security
  • fast communication
• disadvantages of networks

  • increased security risk -> malware spreads
  • of server fails computers might not work
  • computer can run slow if there’s large amounts of data
• what is bandwidth


  how much data can be sent/recived in a given time(measured in bits per second)
• how to calculate number of colours in an image


  2^n (n is colour depth)
• what is colour depth


  number of bits per pixel