GCSE Computer Science (OCR)

• Arithmetic Logic Unit (ALU)


  Performs operations on data e.g. Addition, subtraction
• Control Unit (CU)


  Coordinating activities of the CPU
• Registers


  Quick, small stores of data within the CPU
• Memory Address Register (MAR)


  Holds memory address for data or a instruction about to be used by the CPU
• Memory Data Register (MDR)


  Holds actual data or instruction
• Accumulator


  Stores results of calculations in the ALU
• Program Counter (PC)


  Holds memory address of the instruction for each cycle
• Fetch


  The next instruction is retrieved by CPU from main memory
• Decode


  The instruction is broken down and decided so computer can understand
• Execute


  The CPU performs what the instructions told
• Embedded System


  A computer system built within a large device e.g. Camera, washer, car
• Volatile


  Memory loses its data when power of
• Non-volatile


  Memory retains its data when power is lost
• Random Access Memory (RAM)


  Read/write - function is to load open programs and operating system data currently in use - volatile
• Read Only Memory (ROM)


  Can only be read, can't be changed, stores essential programs to be run in order to boot the computer - non-volatile
• Cache

  A type memory that stores copies of frequently used data, much faster than RAM, lower capacity - closer to CPU
• Buses


  Collection of wires that carry signals between various components of the computer system
• Central Processing Unit (CPU)


  Processes all of the data and instructions that make the system work - can be effected by clock speed, number of cores, cache size
• Clock speed

  How fast the computer does the FDE cycle
• virtual memory


  A memory management procedure needed when the RAM is full so a temporary section is made which acts like a part of RAM
• Flash memory

  Solid state storage, non-volatile, more reliable/durable but can only be overwritten a limited number of times
• Graphics Processing Unit (GPU)


  Handles graphics and image processing
• Optical storage

  CD, DVD, Blue-rayADV: cheap,easy to transportDIS: slow, less storage than hard drives, stored data degrades over time, cannot be written over
• Magnetic storage

  Hard drivesADV: fast access, stores large amounts of data, low costDIS: not very portable, easily be broken
• Solid State storage


  USB, flash memory, SDADV: fast, small, light, easily potable, quietDIS: more expensive, storage capacity less, limited number erase/write cycles
• Cloud stotage

  Data is stored on multiple servers in a remote locationADV: secure, can be accessed anywhere, no need to buyDIS: needs internet, download and upload can be effected by internet connection, less control if data is held
• Operating System


  essential software that links the hardware and other software together and generally manages the computer system
• Command-line Interface


  Text commands where user has to type in command
• Graphical User Interface (GUI)


  uses icons and other visual indicators to navigate and issue commands
• Utility Software

  maintains a computer
• Defragmentation Software


  reorganises data on the hard drive to put fragmented files back together and moves files to collect all the free space
• Backup Software

  Full Backup - a copy is taken from from every file on the system Incremental Backup - only files created or edited since last backup are copied
• Compression Software

  reduces file size so they take up less space on hard disk
• Encryption Software


  scrambles data to stop others from accessing it
• Open Source Software


  source code is made freely available and users can modify itADV: free, ,made for greater good, can be adapted DIS: small, buggy, security holes, no warranties, no customer support
• Proprietary Software


  only the compiled code is released and the source code is kept a secretADV: warranties, well-tested, reliable, cheaperDIS: expensive, software may not fit user needs
• Personal Area Network (PAN)


  within the range of an individual person
• Local Area Network (LAN)


  a network that connects devices close to each other e.g. school, house
• Wide Area Network (WAN)


  a network within a large geographical area e.g. internet
• Bandwidth


  amount of data that can be transferred in a given time