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I just received the Western Digital Caviar Green (WD5000AADS). I noticed it has a jumper setting "Spread Spectrum Clocking". I read somewhere this is a trade-off between speed and reduced electromagnetic noise.

  1. Is that understanding accurate, or what is the setting for exactly?
  2. Why should I consider enabling it? (I have two other hard disks that will be nearby, if this makes a difference.)
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See this – Moab Oct 5 '11 at 3:57
up vote 4 down vote accepted

Many hardware devices that put out enough electromagnetic interference, or EMI, to interfere with the reception of TVs and radios have a feature known as spread spectrum clocking (SSC). However, SSC is not well understood by many people. It is usually disabled by default. You have the option of turning it on or off, but it's best to leave it disabled. Digital systems such as computers synchronize the activity of multiple elements through the use of a clock signal or a pulse. This signal usually exists in a narrow band of frequencies. If it's intense enough at those frequencies, it can violate FCC rules about how much EMI a device rated for certain use can put out.

SSC tries to get around this problem by shaping the emissions -- i.e., varying the frequencies used -- so that instead of the clock using one narrow frequency range, it's spread out over a number of different ones at a much lower

Source Of information

Other resources

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The and links are most relevant/trustworthy for me, I think. Plus this link ( from Psycogeek's answer. The best answer for me would cite just those three, but your answer comes the closest. – DuckMaestro Oct 10 '11 at 21:53

It really depends if you need to use it or not. If you will be using sensitive equipment such as in a lab with the computer then you should use the SSC. Otherwise it will not really make a difference for you and you'll sacrifice a bit of speed.

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I would leave it as it came to me, unless I had special needs, then I would change it.

I do not believe that in this situation that any speed difference could ever be seen between the two different settings, even after advanced benchmarking repeatedly and averaging the results.

SATA Hard Drive Jumper Settings WD SATA

WD SATA hard drives are factory set for workstation/desktop use. For enterprise storage requirements, the jumpers can be set to enable spread spectrum clocking or power-up in standby modes. WD SATA drives are shipped from the factory either with or without a jumper shunt in the spread spectrum clocking (SSC) enable/disable position (on pins 1 and 2). It is not necessary to add or remove the jumper shunt on the drive for workstation/desktop use. For enterprise storage enviroments, use the following advanced settings:

SSC Mode (Default 1): spread spectrum clocking feature enabled or disabled. Default 1 setting is disabled or jumper shunt placed on pins 1–2. Removing the jumper enables the spread spectrum clocking feature.

SSC Mode (Default 2): spread spectrum clocking feature enabled or disabled. Default 2 setting is disabled or no jumper shunt placed on pins 1–2. Adding the jumper to pins 1–2 enables the spread spectrum clocking feature.

Who writes this stuff! I still cannot read it the way it is in the original document (last sentence looks incorrect)... Put the jumper on 1-2 to disable SSC Would that be so hard to say?

In rare situtions where there might be a frequency issue based on country, with stuff similar to this (not nessiarily this) they will often ship to that country with it set to work in that country or location.

G5 Mac Issue with SSC

Last week there were several posts on problems with SerialATA hard drives with SSC (Spread Spectrum Clocking) enabled when using the onboard G5 SATA and with some (not all) Mac PCI SATA cards. . . . . . . . . . . . . . . . . . . . . . . . . . . . .

We and Firmtek have found problems with certain SATA drives which have SSC turned on and therefore will NOT work


Users thinking thier Seagate hard drive is Dead or DOA in situations, they used a Segate utility to disable SSC.

and the opposite apparently:

Some users have been using other brands of HDD’s (in RAID configurations) on the Intel Matrix Storage with the ICH7R on the 945 and 955 chipset and have reported that the system crashes during the installation with a BSOD. They have blamed the motherboard and memory but this is not the case. This is because SSC is disabled on the HDD.

and again:

Seagate forum

It seems as if all the controllers that have problems with SSC-enabled drives are RAID controllers

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