Fetch, Decode, Execute

Control unit (CU) - Coordinates the activities of the CPU
Arithmetic logic unit (ALU)  - The ALU performs arithmetic and logical operations on the data. 

Address bus - access a specific memory location (in the RAM). the address is sent to memory on the address bus. 

Data bus - The data in that memory location is then returned to the CPU on the Data Bus. 

Control bus - Control signals are sent along the Control Bus. 

Memory address register (MAR) - Stores the address of the data (or instruction) that is to be fetched or the address that the data is to be written to. 

Program counter (PC) - The program counter holds the address of the next instruction to be executed. 

Memory data register (MDR) - Stores the data that is to be sent to, or fetched from the memory. 

Current instruction register (CIR) - Holds the current instruction being executed, divided into operand and opcode. 

Accumulator (Acc) - Stores the result of the Arithmetic / Logic Unit.