nforce 780 sli MB

Hi,

I wonder if anyone can help. There are a few terms in the System Clocks section of the bios that I am unsure about..

SPP <--> MCP ref. Clock

This is set to auto at the moment, but can be set manually from 200Mhz upwards in 1 MHz increments. What does this actually do?

HT Spread Spectrum
PCIe Spread Spectrum
SATA Spread Spectrum

All disabled at the moment, again, what are these???

Any help appreciated

Bagpus