A Level Computer Science

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CPU:

Carries out all the instructions in a computer.

Made up of billions of transistors.

Clock speed is used to measure the speed at which the CPU works.

Clock speed is measured in Gigahertz.

Registers are memory locations within the processor and they have extremely fast working speeds.

Program Counter (PC);

Keeps track of memory location of the line of machine code being executed.

Counter gets incremented after each fetch-decode cycle.

Changed by instructions which alter the flow of code.

Memory Data Register (MDR):

Stores the data that has been fetched from or stored in.

Stores the content of the memory address.

Memory Address Register (MAR):

Stored the address of the data or instructions which are to be fetched from or stored into.

Current Instruction Register (CIR):

Stores the most recently fetched instruction, waiting to be decoded and executed.