Stops execution of instructions.

Acknowledges interrupt and branches of subroutine.

Acknowledges interrupt and continues.

Acknowledges interrupt and waits for the next instrution from the interrupting device.

make the processor wait during a DMA operation

make the processor wait during an interrupt processing

make the processor wait during a power shutdown

interface slow peripherals to the processor

I/O devices have 16 bit addresses

I/O devices are accessed using IN and OUT instructions

there can be a maximum of 256 input devices and 256 output devices

arithmetic and logic operations can be directly performed with the I/O data.

Memory space available is greater.

Not all data tranfer instructions are available

I/O and Memory address spaces are distinct.

I/O address space is greater.