1.1 Systems Architecture Flashcards
Purpose of the CPU
The processor is like a brain. It controls all the processing of the computer. It does this by using the Fetch-Decode-Execute cycle.
What happens at fetch?
The instruction stored at the memory address in the PC is fetched. The memory address is copied to the MAR.
The contents at the address are fetched into the MDR. The PC is now incremented.
What happens at decode?
The instruction is copied from the MDR to the CU. The CU decodes the instruction and turns it into a series of signals.
If more data is required, then the CU will send out signals to fetch the data.
What happens at execute?
The CU sends out signals to the relevant components to execute the instruction.
4 common CPU components
ALU, CU, cache, registers
Function of the ALU
Carry out logical, shift, arithmetic operations
Function of the CU
Co-ordinates all the activity:
Controls execution, decodes instructions, controls processer timing, sends and receives control signals
Function of cache
Cache is a memory bank that is very fast sits between the CPU and main memory. It is used to temporarily hold instructions and data that the CPU is likely to reuse.
Function of the registers
A register is a special very fast memory location within the CPU used in the execution of instructions.
4 registers
Memory address register, memory data register, program counter, accumulator
Function of the memory address register
Holds the address (location in memory) of the instruction or piece of data to be fetched or executed.
Function of the memory data register
Holds data or a program instruction temporarily when it is fetched from memory or is to be sent to memory.
Function of the program counter
Holds the memory address of the next instruction to be processed.
Function of the accumulator
A special purpose, memory location in which results of operations carried out in the ALU are temporarily stored.
3 characteristics that affect CPU’s performance
Clock speed, cache size, number of cores
