Dit heb ik gevonden
Spread Spectrum Modulated
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There are techniques (developed by the US government, amongst others) for collecting intelligence from PC transmissions, as microprocessors (and screens) can radiate for some distance-you can expect to receive a PC's signals for up to half a mile, and a mainframe's for anywhere between 3-4 (scan the area between 2-12 MHz).
This setting is for Electromagnetic Compatibility (EMC) purposes, based on the idea that harmonic waves generated by bus activity may interfere with the signals that generated them in the first place. Otherwise, as mentioned above, electrical components running at very high frequencies will interfere with others nearby, hence the FCC rules.
This setting gets around the FCC by reducing EMI radiations with slightly staggered normally synchronous clocks, the idea being to lower the peak levels at multiples of the clock frequency by sending a wider, weaker pulse - in other words, the pulse spikes are reduced to flatter curves. It may also stop the sending of clock signals to unused memory sockets (see Auto Detect DIMM/PCI Clk, below). However, some high performance peripheral devices might stop working reliably because of timing problems. This means that, although the energy is the same, the FCC detection instruments only see about a quarter of what they should, since the energy is spread over a wider bandwidth than they can cope with. It is therefore possible that your PC is emitting much more EMI than you expect.
Older boards either centered around the nominal value or were set with the nominal frequency as the maximum (low modulation). Most current ones use the centered method.
The settings could be 1.5% Down, 0.6% Down, 1.5% Center or Disabled (the percentage is the amount of jitter, or variation performed on the clock frequency). Center means centered on the nominal frequency. Shuttle recommends 1.5% Down for the HOT631, but others allow enabling or disabling. The latter may be worth trying if your PC crashes intermittently, as there may be interference with clock multiplying CPUs that phase lock the multiplied CPU clock to the bus clock-if the frequency spread exceeds the lock range, the CPU could malfunction - even a .5% modulation up or down with today's frequencies can vary the bus speed by as much as 10 MHz inside one modulation cycle. In other words, disable when overclocking, because this setting may change the bus speed. In addition, the FSB setting could be cancelled out due to a pin address overlap on the clock generator chip.
You may get a Smart Clock option, which turns off the AGP, PCI and SDRAM clock signals when not in use instead of modulating the frequency of the pulses over time, so EMI can be reduced without compromising stability. It also helps reduce power consumption.
bron =
http://www.electrocution.com/biosc.htm#SPREAD
Maar mijn engels is te beroerd hiervoor om er echt wijs uit te worden..
Iemand die goed technisch engels kan lezen?