paper 1

• Purpose of the CPU

  To fetch, decode and execute instructions
• CPU

  The brain of the computer, takes an input, processes data and produces an output
• Fetch-Execute Cycle

  The cycle the CPU runs through billions of times per second to make a computer work
• CPU

  • Made up of components and registers
• Computer operation

  1. Takes an input

  2. Processes the input

  3. Delivers an output for the user
• Input

  • Clicking a button on the gamepad
• Processing


  The CPU inside the console follows a set of instructions to carry out the task
• Output


  • The player moving on screen
• Fetch stage

  1. The next instruction or data must be fetched from the computer's memory (RAM)

  2. The instruction or data is brought back to the CPU
• Decode stage

  1. The CPU needs to work out what is required from the instruction

  2. This could be a range of tasks depending on what the instruction or data included
• Execute stage

  1. The CPU will carry out the instruction that was fetched

  2. Performing a calculation

  3. Storing a result or data back in main memory (RAM)

  4. Going to main memory to fetch data from a different location
• Key components of the CPU

  • Arithmetic Logic Unit (ALU)
  • Control Unit (CU)
  • Cache
  • Registers
• Each of the components sits within the CPU
• Function of the Arithmetic Logic Unit (ALU)


  1. Performs arithmetic operations

  2. Performs logical decisions
• Function of the Control Unit (CU)

  1. Coordinates how data moves around the CPU by sending a signal to control the movement of the data

  2. Decodes the instructions fetched from memory
• Cache

  Very small, very fast memory located in the CPU which is used to provide quick access to frequently used instructions and data
• Cache

  • The more cache there is, the more data can be stored, which speeds up the performance of the CPU
  • It prevents the CPU from having to repeatedly fetch frequently used instructions from RAM
• Registers

  • Extremely small, extremely fast memory located in the CPU
  • Each register has its very own specific purpose
• Von Neumann Architecture


  A design of the CPU which was proposed by Mathematician John Von Neumann in the 1940s, which most general-purpose computers are built upon
• Von Neumann Architecture

  • Outlines how the computer memory, input / output devices and processor all work together
• Registers in Von Neumann Architecture

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

  • Holds the memory address of the next instructions to be executed
  • Increments by 1 as the fetch-decode-execute cycle runs
• Memory Address Register (MAR)


  Holds the memory address of where data or instructions are to be fetched from
• Memory Data Register (MDR)


  Stores the data or instruction which has been fetched from memory
• Accumulator (ACC)


  Stores the results of any calculations that have taken place in the Arithmetic Logic Unit (ALU)
• Clock speed


  The number of fetch-decode-execute cycles that can take place in 1 second
• Hertz (Hz)


  The unit used to measure clock speed
• Faster clock speed

  More instructions can be fetched and executed per second
• Gigahertz (GHz)


  The unit used to measure modern computer clock speeds, meaning billion
• A clock speed of 3.5GHz can perform up to 3.5 billion instructions per second
• Cache

  Very small, very fast memory on or close to the CPU, used as temporary storage to provide quick access to frequently used instructions and data
• Larger cache size

  More frequently used instructions or data can be stored, resulting in fewer fetch cycles from memory (RAM) and faster performance
• Cache read/write speed

  Significantly faster than RAM, making it much quicker to retrieve instructions from there instead of from memory (RAM)
• Core


  A separate processing unit that can fetch, decode and execute instructions at the same time
• Multi-core processors


  • Have multiple separate processing units that can fetch, decode and execute instructions at the same time
  • Can run more powerful programs with greater ease
  • Increase the performance of the CPU by working with the clock speed
• Network

  More than one computer system connected together allowing for communication and sharing of resources
• Network types

  • Local Area Network
  • Wide Area Network
  • Client-Server Network
  • Peer-to-Peer Network
• Local Area Network (LAN)

  Computer systems situated geographically close together, usually within the same building or small site, like a school or office
• Wide Area Network (WAN)


  Computer systems situated geographically distant to each other, possibly across a country or even across the world
• Client-Server Network

  Clients make requests to a server, the server manages that request and responds