PCI Express Spread Spectrum

[HybridSquirrel]

what does this do? and what should the default setting be? my mobo says down spread

 

[AstroGuardian]

the situation is like this.

When some components have a working frequency like CPU, PCI-E clock generator, GPU etc, the cause electricity to be induced in surrounding metal parts.
This means that sometimes the magnetic field which these components generate, can interfere and cause problems with surrounding components.

Spread spectrum kinda neutralizes these interferences and obtains stable operartion.

However this kind of situations are very rare (unless your computer is placed unprotected near the North or South poles where this megnetic field is generated by the Earth itself) and the spread spectrum should be disabled. I even think that is scarifies a little performance. BUT, if you overclock than all spread spectrums MUST be DISABLED.

 

[AstroGuardian]

Originally posted by: AstroGuardian
the situation is like this.

When some components have a working frequency like CPU, PCI-E clock generator, GPU etc, the cause electricity to be induced in surrounding metal parts.
This means that sometimes the magnetic field which these components generate, can interfere and cause problems with surrounding components.

Spread spectrum kinda neutralizes these interferences and obtains stable operartion.

However this kind of situations are very rare (unless your computer is placed unprotected near the North or South poles where this megnetic field is generated by the Earth itself) and the spread spectrum should be disabled. I even think that is scarifies a little performance. BUT, if you overclock than all spread spectrums MUST be DISABLED.

I am not a professional in these things and i hope i said this the right way. Correct me but the point is OK.

 

[HybridSquirrel]

you know alot more than i know

 

[beer]

Originally posted by: AstroGuardian

Originally posted by: AstroGuardian
the situation is like this.

When some components have a working frequency like CPU, PCI-E clock generator, GPU etc, the cause electricity to be induced in surrounding metal parts.
This means that sometimes the magnetic field which these components generate, can interfere and cause problems with surrounding components.

Spread spectrum kinda neutralizes these interferences and obtains stable operartion.

However this kind of situations are very rare (unless your computer is placed unprotected near the North or South poles where this megnetic field is generated by the Earth itself) and the spread spectrum should be disabled. I even think that is scarifies a little performance. BUT, if you overclock than all spread spectrums MUST be DISABLED.

I am not a professional in these things and i hope i said this the right way. Correct me but the point is OK.

Not really.
Here's the deal - the FCC certifies all preassembled PCs (Dell, HP, etc) under 'regulatory' testing. Such regulatory testing requires that the pc, as a box, emits radiation below a certain intensity threshold. Spread spectrum is used to reduce the peak emission at 2.485 GHz, which is I believe the center frequency for PCI-E clock operation operation, and spread it over a range of frequencies, centered about 2.485, such that the median frequently is still 2.485 but might vary from 2.475 to 2.495 (for example - these figures aren't accurate).

From an engineering point of view, a non-spread clock is a point (delta) function. Spread spectrum takes the energy and puts it into a rectangle, centered about a frequency, with some arbitrary bandwidth. The amount of energy contained (the integral) is the same (spreading doesn't reduce the amount of radiation, just reduces the peak) and regulatory testing is passable.

Also,
the PCI-E clock (which is what you're spreading) can have some unfortunate conflicts with ISM band equipment, such as European 802.11g adapters, where channel 13 can sometimes fall within the clock spread, and channel 14 (only in Japan) that does fall within the spread clock - the pci-e clock can emit radiation that couples within the laptop's antenna connectors, reducing the signal/noise ratio of channel 14 communications, significantly limiting your range.

<-- not a PCI-E PHY designer, but works with them frequently

 

[AstroGuardian]

Aha.... not it is clear to me. But i could swear i read about it somewhere and it was like i was describing it.

But tell me has it anything to do with the thing i wrote before you?

 

[beer]

I have never heard "spread spectrum" and 'magnetic field" mentioned anywhere in the same sentence - I don't really know what you were trying to get at. Magnetic fields are too weak since the clock itself is such a small current draw (relative to other things). Your other point is misleading as well. You don't induce electricity, you can induce interference (at the frequency of the clock) and cause harmonics (at multiples of the core fundamental frequency), and while SS does reduce the harmonic peaks, they reduce it so that you pass Regulatory, and not to prevent interference. There's not much that you interfere with at harmonic for a PCIE clock since they're multiples of 2.4 GHz

 

[40sTheme]

Yeah, to cause interference with most things, the actual waves would have to find a medium outside of your computer in order to travel as well.