Computer Organization

Input-Output (continued)

Communicating with machines is slow (compared to internal operations) because ...
- it may involve mechanical parts (e.g., disks, tape drives).
- it may involve shared, inexpensive (slow) resources (e.g., local area networks, phone lines, modems).
Communicating with humans is very slow for obvious reasons.
I-O controllers are separate, special purpose computers that handle the details of I-O for a particular device; they can receive data and instructions from the CPU, carry out operations independently (in parallel), and report back, allowing the CPU to do lots of other useful work in the meantime.
Storage devices are devices that are capable of both input and output. While such devices are in one package they generally have totally separate internal input and output systems.