________________
|  ALU    | CU  |
|_______________|
|PC   PS        |
|SP         MAR |
|IR         MDR |
|               |
|R0   R1    R2  |
|R3   R4    R5  |
|_______________|
  Typical CPU

ALU - Arithmetic/Logic Unit;  
CU - Control Unit
PC - Program Counter; 
PS - Processor Status Register
SP - Stack Pointer Register
IR - Instruction Register
MAR - Memory Address Register; 
MDR - Memory Data Register
R0, R1, etc. - general purpose Registers