CPU and performance

• Factors affecting CPU performance

  Clock speed

  Cache size

  Number of cores
• What is clock speed measure in?

  Hertz
• What is clock speed?

  Number of fetch decode execute cycles a second
• What is cache

  High speed memory used by the CPU
• What is the number of cores

  number of independent processors in the CPU working together
• What is a core?

  an independent processor in the CPU
• A higher number of cores means...

  better performance as it can multitask
• Describe the Von Neumann architecture

  a system where data and programs/instructions are stored in the same memory location
• What is fetch-decode-execute?

  The process of fetching instructions from memory, decoding and then executing them
• What does ALU stand for

  Arithmetic and logic unit
• What does MDR stand for

  Memory data register
• What does MAR stand for

  Memory address register
• What does ACC stand for

  Accumulator
• What does PC stand for

  Program counter
• What does the CU do?

  Controls flow of data
• What does the ALU do?

  Does all calculations
• Name 3 types of calculations the ALU does

  simple addition, multiplication, division and subtraction
• What does the CPU process?

  data and instructions
• What are the three main parts of the CPU?


  Control unit

  arithmetic and logic unit

  cache
• What does the CU do?

  Manages fetching decoding and execution of program instructions and the flow of data.
• What does the ALU do?

  Does all calculations and contains the accumulator register.
• What is the cache and what does it do?

  Very fast memory in the CPU that stores regularly used data so it can be accessed quickly.
• Caches have low capacity and are expensive compared to RAM, but is faster than RAM.
• What does the program counter do?

  Holds the memory address of the instruction for each cycle.
• Where is the PC located?

  In the control unit.
• What does the accumulator do?

  Stores intermediate results of calculations.
• Where is the accumulator located?

  ALU
• What does the memory address register do?

  Holds any memory address about to be used by the CPU. The address might point to data or a CPU instruction.
• Name the two registers.

  MAR

  MDR
• What does the memory data register do?

  Holds the actual data or instruction.
• What happens in the fetch part of the FDE cycle?

  Memory address copied from PC to MAR

  Copy instruction from MAR to MDR

  Increment PC to point to the address of the next instruction
• What happens in the decode part of the FDE cycle?


  Instruction in MDR is decoded by CU

  CU prepares for next step
• What happens in the execute part of the FDE cycle?

  The instruction is performed
• Name 3 factors that affect CPU performance.

  Clock speed

  Number of cores

  Cache size
• What is clock speed?


  The number of instructions a single processor core can carry out per second.
• What is being overclocked?


  Making the clock speed run at a higher speed than the factory-set rate. Can cause overheating or permanent damage.
• What does a core do?


  Processes data independently from the rest. The more cores, the more instructions it can carry out at once.
• What is cache?


  Data storage inside CPU.
• Why might performance not increase even when core number is doubled?


  The software needs to be designed to use multicore processing.
• What are GPUs?


  Graphics processing units are specialised circuits for handling graphics and image processing.