cpu component

• General-purpose computer system


  Consists of a processor, memory, I/O functionality
• General comp needs:

  • Input: take in data from the outside world
  • Output: display data for humans' understanding
  • Primary storage: computer's main memory which stores a set of critical program's instructions & data
  • Secondary storage: non-volatile storage for noncritical data that will not be frequently accessed
  • Removable secondary storage
• Removable secondary storage


  • File backup and archive
  • Portable transfer of files to second device
• Embedded system


  • Small computer systems, e.g has microprocessors, often a part of a larger system
  • Perform few dedicated, specific functions, w/ dedicated hardware
  • Unlike general-purpose computers used to perform multiple diff functions
• Devices with embedded systems

  • Domestic appliances (freezer), cars, security systems, lighting systems or vending machines
• Role of CPU

  Processes instructions and data that are input into computer so that result can be output
• Microprocessor


  Type of integrated circuit on a single chip
• Stored program concept


  • Instructions and data stored in main memory
  • Instructions fetched and executed in order
• Arithmetic and Logic Unit (ALU)

  • Processes and calculates arithmetic or logical operations
• Control Unit (CU)

  • Controls operation of memory, processor and input/output devices
  • Fetches instructions from memory, decodes them & synchronizes operations before sending signals to computer's memory, ALU and I/O devices to direct how to respond to instructions sent to processor
  • Sends control signals by control buses to control flow of data through CPU
  • Synchronise FE cycle
  • Manage execution of instructions in CPU
• Registers


  Smallest unit of storage of microprocessor; allows fast data transfer between other registers
• Program Counter (PC)

  • Increments the value of the instructions by 1 and fetches+stores address of next instruction to be fetched/processed
• Memory Address Register (MAR)

  • Stores the Address of the instruction/about to be fetched
  • Copies it and sends to MDR
• Memory Data Register (MDR)


  • Stores the Data from the address received from the MAR/has been fetched IS IN USE
  • Sends data to CIR
• Current Instruction Register (CIR)

  • Once program instruction fetched, it is stored in CIR and allows the processor to decode (processed by ALU) & executed (send to bios)
• Accumulator (ACC)

  • Stores interim calculation values of arithmetic & logical operations of ALU
• Buses


  Set of parallel wires that allow the transfer data between components in a computer system
• Data bus


  • Bidirectional, carries data/instructions between cpu components (processor, memory, and I/O devices)
• Address bus


  • Unidirectional, carries address of (main memory location or input/output device about to be used,) from processor to memory address register (MAR)/between components
• Control Bus


  • Unidirectional and bi-directional, transmit control signals from control unit to other cpu components, ensure access/use of data & address buses by components of system does not lead to conflict
• Fetch stage


  • PC holds address of next instruction to be fetched
  • Address bus transfers address -> Memory address register (MAR)
  • MAR uses an address bus to retrieve the instruction in the address
  • Once MAR received, a data bus sends instructions -> Memory data register
  • Once MDR received, MDR uses a data bus to send instructions to the CIR within the CU
• Decode stage


  CU decode instruction using an instruction set
• Execute stage


  • Instructions executed by the control unit sending control signals using control buses
  • If instructions involve calculations -> ALU
• Instruction set


  List of all commands that can be processed by a CPU, machine code
• Process of fetch-decode-execute cycle and role of each component

  1. Instructions and data are fetched from RAM into the CPU, processed using each component then executed

  2. Storing data and addresses into specific registers

  3. Using buses to transmit data, addresses and signals

  4. Using units to fetch, decode and execute data instructions
• Core


  • Processing unit of CPU/ perform FDE cyce/ process/execute an instruction
  • Increase cores -> process more cycles at a time -> increase CPU performance
• Cache


  • Cache memory located within CPU stores frequently used/current instructions and data that needs to be accessed faster
  • Increase cache size -> more data can be accessed faster -> increase CPU performance
• Clock

  • The clock defines the clock cycle that synchronises all computer operations
  • Controls the rate at which program instructions are carried out, by sending electrical signals at regular intervals, called cycles
  • Clock speed: max number of FDE cycles CPU can execute in second
  • Increase clock speed(Hz)-> increase processing speed -> CPU performance
  • Overclocking leads to operations becoming un-synchronised and overheating of CPU