I/O Interface
I/O devices share the memory address space
Control registers manipulated just like memory word
Read/write register to initiate I/O operation
Programs periodically checks whether I/O has completed
Device signals CPU when operation is complete
Software must take over to handle the data transfers from the device
Check for interrupt pending before fetching next instruction
Save PC & vector to special memory location for next instruction
Instruction set includes a "return from interrupt" instruction