CPU from Operating Systems Perspective: terminology

• Register: a fast memory cell inside of the CPU
• PC - Program Counter: address of an instruction to be fetched
• IR - Instruction Register: contains the most recent fetched instruction
• MAR - Memory Address Register: next address to read or write
• MBR - Memory Buffer Register: contains data to be written to memory, or receives the data read from memory
• I/OAR - I/O Address Register: address of an I/O
• I/OBR - I/O Buffer Register: used for exchange of data between an I/O and the processor