The CPU is designed to treat all peripheral, I/O, and memory locations identically as addresses in the 64 Kbyte memory map. This is referred to as memory- mapped I/O. There are no special instructions for I/O that are separate from those used for memory. This architecture also allows accessing an operand from an external memory location with no execution-time penalty.
The CPU registers are an integral part of the CPU and are not addressed as memory locations. The seven registers are shown in Figure 2.
