Registers
Computer Science: OCR A Level, topic 1.1.2
Registers of the Central Processing Unit (CPU)
Registers that have a predetermined purpose in the central processing unit are known as special purpose registers.
Program Counter (PC)
- Holds the memory location address of the next instruction to be performed by the CPU.
- The PC does not store the instruction itself.
Accumulator (ACC)
- Holds the result of calculations and operations performed by the arithmetic logic unit (ALU).
Memory Address Register (MAR)
- Holds the address of the location in memory where data is to be retrieved or stored.
Memory Data Register (MDR)
- Holds the data that has been retrieved from memory, or that is about to be stored in memory.
Current Instruction Register (CIR)
- The Current Instruction Register (CIR) is used to store the current instruction that the CPU is working on.
Test yourself on Registers
What is the purpose of the program counter?
In which register is the output of the arithmetic and logic unit stored?
In which register is the current instruction that the CPU is working on stored?