Systems Architecture

• What does the CPU stand for?

  Central Processing Unit
• What is the purpose of the CPU?

  To fetch, decode and execute instructions OR to process data.
• How does a computer carry out instructions?

  The fetch-execute cycle
• What happens in the fetch stage?


  The CPU fetches an instruction from main memory (RAM).
• What happens in the decode stage?

  The CU inspects instructions.
• What happens in the execute stage?

  The decoded instruction is carried out.
• On a modern CPU, how many times does the FDE cycle occur?

  Billions of times per second
• What is clock speed?

  The speed a CPU can process instructions
• What is clock speed measured in?

  Hertz
• How many Hertz are in a GHz?

  1 billion
• What does ALU stand for?

  Arithmetic Logic Unit
• What does the ALU do?

  Performs arithmetic calculations and logical decisions
• What does the CU stand for?

  Control Unit
• What does the CU do?

  It sends signals to control how data moves around the CPU
• What are the two main components of the CPU?

  ALU and CU
• What is cache?

  A piece of small, temporary memory located in the CPU
• What is the purpose of cache?

  To provide fast access to frequently used instructions
• Why is cache quicker than main memory?

  It is closer to the CPU
• What are registers?

  Small, fast pieces of memory inside the CPU.
• What are the 4 registers?

  ACC, MAR, MDR, PC
• What does ACC stand for?

  Accumulator
• What does MAR stand for?

  Memory Address Register
• What does MDR stand for?

  Memory Data Register
• What does PC stand for?

  Program Counter
• What does the ACC do?

  Stores results from calculations until they are written to the main memory (RAM).
• What does the MAR do?

  Holds the address of the current instruction to be stored to or fetched from memory
• What does the MDR do?

  Holds the data that needs to be written to or fetched from main memory
• What does the PC do?

  Holds the address of the next instruction