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• Hardware

  The physical stuff in a computer system e.g. keyboard, CPU, etc
• Software

  The programs that a computer system runs, e.g. operating system, games, web browsers, etc
• Embedded Systems


  Computers built into other devices, usually as control systems e.g. they could control: dishwashers, microwaves, sat navs
• Embedded systems

  • Easier to design
  • Cheaper to use
  • More efficient (at their task than general purpose systems)
• Central Processing Unit (CPU)


  Where a computer processes all data and instructions
• Control Unit (CU)


  Controls the flow of data in and out of the CPU; manages the fetching, decoding and execution of instructions
• Arithmetic Logic Unit (ALU)


  Does calculations e.g. addition, subtraction, multiplication, division; also performs binary shifts and logic operations
• Cache


  Stores regularly used data for quick access; low capacity and expensive; 3 levels of cache memory: L1, L2, L3 - decreasing speed, increasing capacity (L1 fastest)
• Registers


  Temporarily hold small amounts of data; extremely fast to read/write to
• 3 factors affecting CPU performance


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

  Cores process data independently so more cores means more instructions can be carried out at once
• Clock speed

  The number of instructions a single processor core can carry out per second
• Cache size

  A larger CPU cache gives the CPU faster access to more data
• Parts of the CPU Von Neumann

  • Control Unit (Program Counter)
  • Arithmetic Logic Unit (Accumulator)
  • Registers (Memory Address Register, Memory Data Register)
• Program Counter (PC)


  Holds the memory address of the instruction for each cycle
• Accumulator


  Stores immediate results of calculation in the ALU
• Memory Address Register (MAR)


  Holds any memory address about to be used by the CPU, could point to data or an instruction
• Memory Data Register (MDR)


  Holds the actual data or instruction, either fetched from memory or waiting to be written to memory
• Memory


  Holds program instructions and data
• Fetch (of fetch-execute cycle)


  1. Memory address copied from the program counter to the MAR

  2. Instruction copied from memory to the MDR

  3. Program counter incremented to point to the next instruction
• Decode (of fetch-execute cycle)


  1. Instruction in the MDR decoded by the control unit

  2. Control unit prepares for next step e.g. by loading values into the MAR or MDR
• Execute (of fetch-execute cycle)


  Decoded instruction carried out, examples: Load data from memory, Write data to memory, Do calculation or logic operation (using the ALU)