1.1.1 Architecture of the CPU

What is the purpose of the CPU?

To process data and instructions by constantly repeating the FDE cycle

What are the steps of the FDE cycle?

Fetch - causes the next instruction and any data involved to be fetched from main memory

Decode - decodes (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?

• to direct/coordinate the CPU’s operation such as the timing of other CPU parts

• receives signals from the system clock and sends timing signals and control signals to other CPU parts such as RAM and ALU

• to decode and execute instructions

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 address of the next instruction to be executed

• 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 temporary storage place for one instruction or address

What is the purpose of the MAR?

• To copy and hold the address of the instruction to be executed from the PC

What is the purpose of the MDR?

• To fetch the instruction at the address in MAR from memory and to copy it to the MDR where it is held

• the CU will decode that instruction and decide of any data needs to be fetched

• if so, the MAR holds the address of the data

• the data is fetched and copied to MDR

What are the key features of Von Neumann architecture?

• program instructions and data the programs are using are both stored in the same memory

• CPU accesses both instructions and data from the same RAM