# What is Spread Spectrum Clocking?



## Brum

I just recently purchased 2 new western digital caviar SE 250GB/16Mb Cache/7200RPM/SATA300 Hard Disk Drives to use in a RAID array with my MSI PM8M-V MS-7104 Motherboard. I have succesfully installed the drives in a RAID0 setup and they work great. 

While I was installing them though, I noticed a jumper where I could set the drives to use spread spectrum clocking. When I googled it I didn't find much except an explanation on how to use it on WD website. The only thing I found that Western Digital said about it was to make sure your motherboard is capable of spread spectrum clocking before you enable it on the HDD. In my stupidity I automatically figured that my cheap old motherboard probably didn't support SSC so I just stuck the HDD in and they worked fine.

A few weeks later, I just noticed in my bois that my computer does have spread spectrum clocking abillities. What is Spread Spectrum Clocking? Why is there a jumper for it on my HDDs? Should I enable it?

Thank you guys for taking the time to read my question. If anyone has any answers or opinions please let me know. Thank you.


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## kronus

Here's a good article.

http://zone.ni.com/devzone/cda/tut/p/id/4154

It looks like you probably wouldn't need to use unless you had some crazy lab with em sensitive equipment or were in a location sensitive to em interference. Can't hurt to turn it on though.


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## Brum

Thank you for the reply,
That article was definitely the closest to my question that I have found. I keep finding stuff about military coding, or wireless communications or some crazy thing.

So, from what I am understanding, it is pretty much pointless? That wasn't a bad article but that doesn't really explain why the jumper is on my HDDs. Would it slow down my system or would it speed it up? I suppose your right, it probably can't hurt to turn it on. I just wish I understood what that article was talking about, lol. It went right over my head. I'm not really sure what they meant by the FCC standard or why it is even a standard either.

Sorry, I'm just still a little clueless.


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## Brum

I found this article that says it reduces electromagnetic interference emissions, (EMI). Whatever that is. It almost sounds like it could put a crutch on my system.

http://www.eetimes.com/in_focus/communications/OEG20030414S0078


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## Brum

I found the definition of EMI and it helps alot.

"EMI is a combination of terms that broadly refers to any type of interference that can potentially disrupt, degrade or otherwise interfere with authorized electronic emissions over approved portions of the electromagnetic spectrum."

By the defenition of spread spectrum clocking that I have determined from reading and research, SSC reduces EMI which disrupts data. I read another definition too that said EMI can cause errors when reading data. Also in the article I posted above it mentioned that SSC reduces the EMIs of the system clock without degrading the timing of the system clock at all. So in theory, SSC should always be turned on when possible becuase it reduces errors without slowing down or hurting the system.

I'm going to try turning it on, but I doubt I notice any difference. If anyone has anything they would like to add please feel free. As I said, this is just my conclusion to the resaerching I have done on it.


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## JohnWill

When testing electronic equipment, there are two types of EMI that are considered, radiated EMI and EMI susceptibility. Radiated is a measure of how much electrical noise you emit, and susceptibility is how sensitive you are to radiated EMI from an external source. Obviously, spread spectrum clocking is attempting to deal with radiated EMI.


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## Fraki

hello there folks,
i discovered those feature at the 500GB WD RE II drives. 
At first thanks for the excellent article about SSC! I also discovered in the data sheet of the drive mentioned above, that this feature should be activated if the drive is used in storage environments.

Has anyone information if this feature must be supported by the motherboard? And if it should be enabled by default?


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## TurboAAA

Does any of this relate to the spread sprectrum clocking of memory and processors? I have those settings in my bios but have not messed with them until I know what they are for.

I remember learning about the clocking for HDs and how you could increase performance at the risk of data damage and interference of other devices in the case.

I'm just curious.


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## Fraki

@TurboAAA: i don't think so. In my opinion it only lowers the electronic interferences to the level given by the FCC.
The clocking of HDDs is untouched by this.


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## Hugh Merr

I'll use very basic terms because I know this forum has computer users of varied experience.

If you have a fast modern computer and/or Overclock, leave Spread Spectrum *OFF!* In your Bios or other equipment like hard drives. In the older days of slow computers, spread spectrum *ON* wasn't a problem.

Computers today are designed to use a very fast clock speed and need a very accurate clock tic to time all the various processing. What spread spectrum does is take the sharp clean tic signal of your clock generator pulse, weakens it and spreads it into a flattened underpowered group of smaller blurred spikes of similar frequencies. Example: Instead of having a solid and clean 3.6GHz processor clock speed you will have a lower powered clock signal *pulsating* "around 3.6GHz". If you know a bit about computers you know that computers need a sharp and accurate clock signal to be the fastest and have the most stable timing. Low CAS DDR Ram timing is the most deeply effected for it uses the rise and fall of a good narrow clock signal to operate quickly. Would it make sense to send it a "weak blurry" spread spectrum signal instead of a crisp, strong, narrow, easy to detect spike?

Spread spectrum ON will reduce the "small possibility" of a very little RFI/EMI but at the expense of a more stable computer. With the weakened and blurred "spread spectrum" of clock signals, faster computers will not OC well. Performance RAM and other parts won't run at their full potential. Overclockers spend most of their time boosting voltage and fine tuning various timings to strengthen and tighten the signal for the cleanest clock signals for the quickest, most stable computer systems. I don't know a home user that would ever need Spread Spectrum ON, unless you're using very RFI/EMI sensitive electronic lab equipment in your home. Maybe if you have a radio telescope in your backyard scanning for life on other planets . . . 

If RFI/EMI was a problem inside the computer case, everything inside would have to be heavily shielded. FCC was mainly concerned about one piece of electronics in the home effecting another piece of electronics. Like if you key the mic on a walkie-talkie near your monitor, the image will distort due to RFI (radio frequency interference). If you hold a magnet near your monitor it will distort the image due to EMI (electro-magnetic interference). As long as your cordless phones, TVs, Stereos, HAM radios, CBs and everything else that edits interference that you own aren't all stacked on top of each other (which would be really dumb), you'll be just fine.

As a Computer Tech, my favorite giggle is when I'm doing an on-site consultation of an unstable computer and seeing that the client has the computers Sub-woofer (huge magnet the size of your fist inside) either right beside or on top of their computer. Now you're talking EMI !!! They'd never stick a small fridge magnet to their computer for fear of corrupting data but most people don't even think about the huge 1lb. magnet in the sub-woofer!! 

Here's two great technical pages that explain what Spread Spectrum is as it relates to computers.
http://zone.ni.com/devzone/cda/tut/p/id/4154
http://searchwincomputing.techtarget.com/tip/0,289483,sid68_gci1189366,00.html

I hope this helps explain to all levels of users.
Hugh Merr. :up:


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## Matthew196

Spread Spectrum Clocking WILL CAUSE performance and lockup issues on a Windows XP Pro computer. So SCC IS NOT A GOOD IDEA to use on computers!!!

It was a bad invention for computers!!! :down:  

I spent 3 months with a Senior Escalation Support Tech at Microsoft trying figure out my problems and the SCC was the HEART of the causes of my problem AND IT TOOK US 3 MONTHS to figure it out!!! . 

But it was myself who finally solved it by experimenting and shut it off in BIOS!!! Which cured ALL my issues!!!:up: 

AS my computer was locking up, giving me blue screen's VERY FRREQUENTLY and about every time it was a different stop error message!!!

This is what the Microsoft tech support rep told me about the dump file the computer was creating because if the SSC!!

"First, I have checked all dump files; the error occurs for win32k.sys and ntps.sys files. Based on my experience, the issue is hardware related."

SSC is HARDWARE RELATED!!!

Plus those 2 files mentioned above are SYSTEM CRITICAL FILES that are required to be working to make Windows XP function properly!!!

So anyone out there that DONT NEED SSC, PLEASE DISABLE IT!!! It will save you MUCH HASSLE!!!!

Just a good recommendation because it gave me a WORLD of problems!!!


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