Computer scienc paper 1

• CPU


  The purpose of the CPU is to carry out the processing of data on the computer system
• Fetch-decode-execute cycle


  CPU fetches, decodes and executes instructions
• CPU performance


  The rate at which instructions are carried out each second
• Clock speed


  Measured in Hertz (Hz), a 3.5 GHz processor carried out 3.6 billion calculations a second
• Cache


  Cache memory is a buffer that sits between the CPU and main memory, the CPU will check here first for instructions that have been fetched before, the larger the cache the more space there is for instructions the CPU needs
• Cache


  • Has similar access speeds to the CPU and is therefore quicker to fetch instructions from
• Cores


  Independent processors in the CPU working together, the higher the number of cores the better performance of the computer as it can multitask
• Registers


  Temporary memory stores within the CPU which have a specific purpose
• Von Neumann architecture


  A system where data and programs/instructions are stored in the same main memory location
• Fetch-decode-execute cycle


  1. Fetch: Stores the address of the instruction/data in the MAR, fetches the instruction from MAR and copies it to MDR

  2. Decode: The instruction in the MDR is copied to the CIR and decoded by the control unit

  3. Execute: The instruction is performed, the ALU may be used for any logic or calculations, the result is stored in the accumulator, the PC is incremented
• Embedded system


  A computer system that is made up of both hardware and software, often known as firmware, usually for very specialised tasks, doesn't usually contain an operating system
• Embedded systems


  • Dishwasher
  • Microwave
  • Fridge
  • Smartphone
  • TV
• RAM


  Volatile memory that can be changed by the computer, the contents are lost when the power is turned off, larger memory capacity compared to ROM
• ROM


  Non-volatile memory that can only be read, the contents are programmed during manufacture and cannot be changed, used to store the boot program and other essential software
• Flash memory


  Non-volatile memory that can be changed and does not need a power supply to keep its contents, has no moving parts which makes it fast and reliable, used in memory cards, USB sticks, and solid state drives
• Virtual memory


  Part of the hard drive used as an extension to RAM if there is not enough RAM to hold all the data and run the programs needed, access speeds are slower than from RAM
• Secondary storage


  Long-term storage for files and data, includes optical, magnetic, and solid state storage
• Types of secondary storage

  • Optical
  • Magnetic
  • Solid state
• Optical storage


  • Good capacity, light and portable, can get damaged, slow access speed
• Magnetic storage


  • High capacity, reliable, slow to read due to moving parts
• Solid state storage


  • No moving parts, very fast access, most are a type of flash memory
• Calculating storage requirements


  Using knowledge of data representation to calculate the size of files and storage needed
• Network

  Two or more computers connected to each other
• Types of networks


  • LAN (Local Area Network)
  • WAN (Wide Area Network)
• LAN

  • Covers a small geographic area, owned by the organisation
• WAN


  • Computers are geographically separated, communication is not owned by the organisation
• Network Interface Card (NIC)


  Any device connected to a network needs an NIC to produce electrical signals for receiving and sending messages, has a unique MAC address
• Switch


  Connects devices together on a LAN, sends data along the network using the MAC address for the destination, only sends data to the intended destination
• Router


  Used to send data between networks and connect devices to the internet
• Wireless Access Point


  Allows wireless devices to connect to a network
• Transmission media


  • Twisted pair cable
  • Coaxial cable
  • Fibre optic
• Twisted pair cable


  • Most common, cheap and easy to install, fast and reliable transmission
• Coaxial cable


  • Bulkier than twisted pair, made of a single copper wire insulated to minimise interference
• Fibre optic


  • Can transmit data as light, high performance, do not suffer from interference, can transmit over large distances but is expensive
• input devices allow data into the computer eg keyboard or mouse