On 2020-03-05, madscientistatlarge <[email protected]> wrote:
> To reduce problems with emitted Radio Frequency Interference, most
> processors now use a clock that varies in speed over time. This
> doesn't really reduce the emitted energy, but because it is always
> changing frequency interference with other devices tends to be
> intermittent, and Ideally unnoticeable. Also the oscillators used
> in computers are not the most precise, they don't need to be and
> precision cost. The bios may let you toggle this deliberate
> frequency variation and off, which I suppose could be critical in
> some real-time cases, or a varying clock may, in some cases cause
> objectionable interference where as the fixed clock, may not, YMMV.
A clock that varies like that is usually referred to has a
"spread-spectrum" clock. If properly implimented it has no measurable
effect on software execution (even for real-time cases) because the
variation is done so that the average frequency is "constant" and the
deviation from that average sums to 0 for any significant period of
time (anything over a few hundred microseconds).
The variation of the average over temperature and supply voltage is
usually far more significant.
--
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