Different kinds of registers are general between most microprocessor designs. These are:
Program Counter (PC)
This register is utilized to hold the memory address of the next instruction that has to executed in a program. This is to ensure the CPU knows at all times where it has reached, that is able to recommence following an execution at the correct point, and that the program is executed properly.
Instruction Register (IR)
This is used to hold the current instruction in the processor while it is being decoded and executed, in turn for the speed of the whole execution process to be reduced. This is because the time required to access the instruction register is much less than continual checking of the memory location itself.
Memory Address Register (MAR)
Used for storage of memory addresses, typically the addresses involved in the instructions held in the instruction register. The control unit then ensures this register when needing to know which memory addresses to check or gain data from.
Accumulator (A, or ACC)
The accumulator is used to store the result of operations performed by the ALU, as enclosed in the section on the ALU.
Memory Buffer Register (MBR)
When an instruction or data is obtained from the memory or elsewhere, it is first to be found in the memory buffer register. The next action to take is then determined and carried out, and the data is moved on to the preferred location.
Other general purpose registers
these registers have no specific reason, but are generally used for the fast storage of pieces of data that are required later in the program execution. In the model used here these are assigned the names A and B, with suffixes of L and U indicating the lower and upper parts of the register correspondingly.
Status flags/ Flag register
the flag register is particularly designed to contain all the appropriate 1-bit status flags, which are changed as a result of operations concerning the arithmetic and logic unit. Further information can be found in the section on the ALU.