Structure + function of a processor Flashcards
What is the CPU
Central Processing Unit - Runs programs by continuously fetching, decoding and executing instructions
What is the ALU
Arithmetic Logic Unit - Carries out the calculations and logical decisions.
What is the CU
Control Unit
- Sends out signals to co-ordinate how the processor works
- It controls how data moves around parts of the CPU and memory
- Instructions are decoded in the control unit
What is a register
A discrete piece of memory built onto the CPU that holds a single piece of data
What is the PC
Program Counter - Keeps track of the location of the line of machine code being executed
What is the MDR
Memory Data Register - Stores the data or instructions that are to be fetched from memory or sent to memory
What is the MAR
Memory Address Register - Stores the address of the data or instructions that are to be fetched from memory or sent to memory
What is the CIR
Current Instruction Register - Stores the most recently fetched instruction, which will be decoded and executed
What is the ACC
Accumulator - Stores the results of calculations made by the ALU
What are buses
The communications channels through which data can be sent around the computer
What is the purpose of the data bus
Carries data between the processor and memory
What is the purpose of the address bus
Carries the address of the memory location being read from or written to
What is the purpose of the control bus
Sends control signals from the control unit
Describe what happens when fetching instructions
- Contents of the PC are copied to the MAR
- The read signal is sent across the control bus and the contents of the MAR are sent across the address bus
- The contents of the memory location stored in the MAR are then sent across the data bus and stored in the MDR
- The contents of the MDR are then copied to the CIR
- The PC is incremented by one
Describe what happens when decoding instructions
- The contents of the CIR are sent to the CU
- The CU then decodes the instruction
Describe what happens when executing instructions
If the instruction is…
- for a memory location to be read from or written then the address stored within the instruction will be loaded into the MAR
- to carry out a calculation then the contents of the MDR and ACC are sent to the ALU and the results are sent back to the ACC
What is the clock speed
The frequency at which the clock generator of a processor can generate pulses
What is a core
A processing unit within the CPU
How does clock speed affect performance
Higher clock speed, the faster the CPU can run and the more instructions that can be processed every second
How does the number of cores affect performance
More cores, easier it is to run more things simultaneously. This means tasks that can share their work will run faster