Architecture of the CPU
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What is the ALU?
Carries out calculations and logical decisions such as +,-,X
What is the CU?
Co-ordinates activity of CPU and memory - decodes instructions
What is Cache?
Temporary storage that can be accessed quickly
Name the registers
ACC, PC, MDR and MAR
What does the ACC do?
Stores results of ALU
What does the PC do?
Keeps track of address and is incremented when fetched
What does the MDR do?
Stores data fetched from memory
What does the MAR do?
Stores address to be used by MDR
What is CU?
Control Unit
What is MDR?
Memory Data Register
What is MAR?
Memory Address Register
What is PC?
Program Counter
What is ACC?
Accumulator
What is the first stage of the fetch part of the cycle?
Address of next instruction copied from PC and placed in MAR
What is the second stage of the fetch part of the cycle?
CU fetches data stored at that address and copies it to MDR
What is the last stage of the fetch part of the cycle?
Increments PC by one
What happens in the decode cycle?
CU decodes the instruction to see what to do next
What happens in the execute cycle?
Decoded instruction is then executed ,e.g ALU performs calculation