a peripheral is anything that is not needed for the core to function. A wii can function without a wiimote. It will be limited but it can function.
A power supply is not a peripheral.
A mobo/processor/ram are not peripherals
some kind of internal memory at least is required, so a hard drive could be a peripheral.
Video processing can be done right on the mobo, so a standalone vid card is a peripheral. Additionally, a computer can run without a video card, it just cannot display images, and not all computers require that either.
an optical drive is one
video card
Hard drive
input
speakers
communications
a good synonym for peripheral is supplemental, as in something that acts as a booster, or something that facilitates existing abilities.
At least that's my take on it.
