Comp Sci CAIE

• HTTP - hypertext transfer protocol


  a set of rules which must be followed when transferring files across the internet
• URL - uniform resource locator


  used to find/identify a webpage on the internet 1. webserver name 2. file name 3. protocol
• web browser


  software that allows a user to display a webpage on their screen - they interpret html code and show the result
• actuator


  used in many control operations involving sensors and ADC/DACs. Electromagnetic device eg. motor that outputs result of sensor operation
• loudspeaker

  output device that produces sound using voltages at different levels which vibrate a cone in speaker housing
• LED


  Used for backlighting a monitor/tv - they are thin, produce a white light, and do not require much power
• CCFL

  Old technology used for backlighting - took time to warm up, and produced yellow-ish lighting + required a lot of power
• volatile


  memory that loses its contents when the power is off eg. main memory
• non-volatile

  memory that doesn't lose its contents when the power is off e.g. hard disk
• off-line storage


  storage that can be physically moved away from a device and stored somewhere else e.g. CD, USB stick, DVD
• SRAM


  type of RAM that has 'flip flops' to hold each bit of memory. Does not need constant refreshing.
• magnetic media


  secondary storage with mechanical parts which move over the surface to read and write data magnetically e.g. a hard disk, tape or floppy disk
• program


  our way of telling a computer what to do, how to do it, and when to do it
• assembly language


  code that is specific to a particular hardware, but needs to be translated into machine code before it can run
• machine code


  the binary code that is specific to a machine and does not need translating in order to run
• translator


  program that changes higher level language into machine code
• compiler


  this translates HLL into machine code. Once it has done this, the program can be used multiple times without translating it again
• UPS


  uninterruptable power supply
• cracking

  editing source code with malicious intent
• firewall


  this examines traffic between a user's computer and the internet by checking what is/isn't allowed and blocking traffic that does not meet certain criteria
• proxy server

  this filters web traffic, keeps the IP address secret, and, using a cache, speeds up access to websites that have been visited before
• TLS - Transport Layer Security


  this is a form of secure data transmission made up of 2 layers: the record protocol, and the handshaking protocol. It is very secure and fairly new, and can make use of session caching, which improves performance. It involves many complicated encryption algorithms. prevents third party hacking into communication between web server and the user's computer.
• session caching


  this is used in TLS to avoid using too much computer time; TLS is able to attempt to resume an existing session, which increases speed.
• Denial of Service (DoS) attack


  attempting to prevent a user from accessing part of a network (usually the server); this is usually temporary, but may be very damaging, or a big security breach. overloads web traffic by sending thousands of requests.
• free software


  software that is free to run, copy, change or adapt, and share with friends, family or colleagues.
• CSS


  Cascading Style Sheet. Controls presentation of page. Enable multiple pages or elements on a page to be changed in one go.
• Gigabyte (GB)


  1024 megabytes. 2 to the power of 30 bytes.
• HTML


  HyperText Mark-up Language. Used to write and develop webpages to present text. Uses tags.
• Terabyte (TB)


  1024 gigabytes. 2 to the power of 40 bytes.
• Lossless image compression

  Find groups of repeating data. Records the data once and the number of times it was repeated.
• Lossless text compression


  Finds patterns in original text. Encodes each pattern in a dictionary
• PNG


  Lossless picture file format that uses alpha channel to keep transparent backgrounds.
• MIDI


  A set of instructions for digital instruments to play synthesised sounds. Musical Instrument Digital Interface.
• .WAV

  uncompressed music files
• .FLAC


  lossless compressed music files
• Parity bit


  Set to 1 or 0. Sent with a byte of data to make the total number of 1s odd or even for each byte.
• 1KB (kilobyte)


  1,024 bytes (2¹⁰ bits)
• 1MB (megabyte)


  (2²⁰ bits)
• 1GB (gigabyte)


  (2³⁰ bits)
• 1TB (terabyte)


  (2⁴⁰ bits)