computer science paper 1 revision flash card

• The CPU is the central processing unit, it carries out program instructions using data
• Components inside the CPU

  • ALU (Arithmetic Logic Unit)
  • Control Unit
  • Cache
  • Registers
• ALU

  Carries out maths and logic needed to execute instructions
• Control Unit


  Coordinates the fetch-execute cycle and decodes instructions
• Cache


  Small, fast memory that holds frequently accessed items
• Special purpose registers


  • Memory Address Register (MAR)
  • Memory Data Register (MDR)
  • Program Counter
  • Accumulator
• MAR


  Holds the address in memory where data/instructions are fetched from or written to
• MDR


  Holds the actual data/instructions that have been fetched from or will be written to memory
• Program Counter


  Holds the address of the next instruction to be fetched
• Accumulator


  Holds the results of ALU calculations
• Von Neumann Architecture


  The structure of a CPU that carries out the fetch-execute cycle
• Fetch-Execute Cycle


  1. Fetch instruction from memory using Program Counter

  2. Decode instruction in Control Unit

  3. Execute instruction, usually using ALU and data from MDR
• Clock speed


  The rate at which the fetch-execute cycle is carried out, measured in GHz
• CPU performance factors


  • Clock speed
  • Number of cores
  • Cache size
• Embedded systems


  Computers built into other devices to perform a specific function
• Types of storage


  • Primary (RAM, ROM)
  • Secondary (Magnetic, Optical, Solid State)
• RAM


  Volatile memory, contents are lost when power is turned off
• ROM


  Non-volatile memory, contains the program that runs when the computer boots up
• Virtual memory


  Part of secondary storage used as an extension of RAM when RAM is full
• Types of secondary storage

  • Magnetic (Hard Disk Drives)
  • Optical (DVDs)
  • Solid State (SSDs)
• Magnetic storage


  • Large capacity, reliable, but fragile and noisy
• Optical storage


  • Portable, reliable, but easily damaged
• Solid state storage


  • Fast, durable, but expensive