I/O means input/output — e.g. input from switch/microphone, output to speaker/motor/whatever
components of a computer system communicate through interconnection network (circuits)
each I/O device appears to processor as addressable locations
implemented as bit storage flip-flops in the form of registers (“I/O registers”)
I/O devices and memory share same address space — “memory-mapped I/O) this means that any instruction which accesses memory can access the device
a device is connected to interconnection network using a circuit — “device interface”
provides means for data transfer, exchange of status & control info