What is FSB Spread spectrum?

Answer 1

ok, after looking on the internet for about an hour i figured out what this is, its a setting to help reduce the EMI that some of these components put out, the way it works (at least to my understanding) is that when , say your CPU is putting out EMI its all concentrated on one "channel/frequency" on the spectrum, what spread spectrum does is broaden that out to multiple channels/frequencies so it isn't as "potent" or interupting.

-AMD Athlon 64 X2 4400+ @ 2.4Ghz
-Abit AN8 Fatal1ty nForce4 SLI
-Ati X1950XTX
-2GB Corsair PC3500 6-2-3-2
-Sound Blaster X-Fi
-WD Raptor X 150



Spread spectrum is a trick used to allow products to pass FCC testing. Inside almost every electronic device is an oscillator of some sort. On a typical motherboard, the front-side-bus may operate at 200MHz. This means that there is a steady 200MHz clock which is running all of the time. This clock runs over long wires. And a long wire carrying a signal is also sometimes known as an antenna.

So, a typical motherboard will be radiating a 200MHz signal into the air as radio waves. Also, there is likely to be a strong 33Mhz and 66Mhz signal from the PCI and AGP ports. Plus, each clock will have overtones which will be odd multiples of the fundamental frequency. So you will also have signals at 100MHz, 167MHz, 200MHz, 233Mhz, etc. Not to mention harmonics plus the noise generated by the signal and control lines.

The problem comes when a product needs FCC certification. On a spectrum analyzer, each of these clock frequencies shows up as a "spike" on the spectrum display. If the spike goes over a certain threshold, the product fails the test. There are several ways to deal with a failure of this type, and they all require making changes in the prduct. Perhaps the board can be re-designed (expensive), or perhaps the case can be improved (possibly also expensive). Or perhaps SS can be turned on (free, if built-in).

SO HOW DOES SPREAD SPECTRUM WORK?
Spread spectrum works by changing the clock frequency. Instead of the FSB running at 200MHZ, it will be AROUND 200MHZ, but constantly varying. One instant it will be 200MHz. The next instant, it will be 199.5MHz, and 198MHz the next, and maybe 202MHz the next. The actual frequency of the clock goes up and down, but is always centered around 200MHz.

Now, if you look at this on a spectrum analyzer, instead of getting a sharp "spike" at 200Mhz, you will get a round "blob" centered at 200MHz. If the top of the blob is below the legal threshold, the product now passes FCC testing. It should be noted that the exact same amount of radio energy is being generated, but the energy has been spread out over a narrow range of frequencies instad of being centered on one frequency. To use a simple analogy, instead of putting $10 on #12 on a roulette wheel, you will instead put $2 on #10, $2 on #11, $2 on #12, $2 on #13, and $2 on #14. This is why it is called "spread spectrum" -- you are taking the same amount of radio energy and spreading it out around the spectrum.

Answer 2

Turning up the Spread spectrum ultimately results in a more stable CPU (fewer crashes) but a slightly slower CPU. I wouldent reccomend turning this option up, because its like trying to get a guitar player to play with fewer strings on his guitar. He can still do a lot, but not near as much as He could with all his strings.