Inside the Processor
Registers are memory locations inside the processor.
PC - Program Counter
Holds the address of the next instruction
ACC - Accumulator
Arithmetic and logic operations happen here
MAR - Memory Address Register
Connects the processor to the address bus. Any address put in here is sent out along the address bus.
MDR - Memory Data Register
Connects the processor to the data bus. Any data put in here is sent out along the data bus. Any data arriving along the data bus ends up in here.
CIR - Current Instruction Register
This is where instructions are decoded and executed.
Arithmetic and Logic Unit
These circuits perform arithmetic and logic operations. The results are put into the accumulator.
The processor used in the OCR version of the Little Man Computer is very out of date. Modern processors do not have a single accumulator, instead they have a number of General Purpose Registers each of which can act like an accumulator.
Does what it says.