Jeremy Nicoll - news posts expressed precisely :
Harry Bloomfield wrote:

If unused for a while, the hard drives in my PC power themselves down,

They do? I could imagine that they might spin down (ie stop rotating) and
therefore reduce their power consumption, but I'd expect their controllers
to stay powered-up, so that they could initiate a spin-up when the next I/O
request comes along.

They do, but having thought about it, its the operating system which
powers it down after a preset period of inactivity.

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Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk