1.1.1 Architecture of the CPU

What is the purpose of the CPU?

To execute instructions by constantly repeating the FDE cycle

What are the steps of the FDE cycle?

Fetch - next instruction and any data involved fetched from main memory (RAM) and brought back to CPU

Decode - understands the instruction

Execute - the instruction is executed (processed/carried out)

The process/cycle is then repeated

What is the function of the control unit?

• sends signals to synchronise/coordinate processes such as the flow of data

• to decode and execute instructions (run F-E cycle)

What is the purpose of the ALU?

• to carry out arithmetic calculations and logic operations

What is the purpose of the PC?

• to hold the memory address of the next instruction to be fetched

• incremented by 1 as soon as that instruction has been fetched

What is the purpose of the ACC?

• to temporarily store arithmetic and logic results from the ALU

What is a register?

• a very fast, very small and temporary storage location on CPU for one instruction or address

What is the purpose of the MAR?

• the address of where the instruction or data is to be fetched from or stored in memory (RAM) is copied from PC (by CU)

• this address is held in MAR

What is the purpose of the MDR?

• holds the instruction at the address in MAR after it has been fetched from RAM and copied to MDR (by CU)

• holds any data to be read from or written to memory as well

What are the key features of Von Neumann architecture?

• first computers were fixed program computers built for a single purpose - to change this purpose you had to rebuild the whole computer.

• Von neumann is stored program – all programs and data stored together in same memory on computer - the purpose can be changed easily