What do my jumpers do?

[MirrorIK]

I have a 74GB Raptor, and the sticker on the top details two positions for the jumper on the back;

1: Jumped pins 1 and 2 disables SSC (Spread Spectrum Clocking) - this is currently jumped.

2: Jumped pins 3 and 4 enables PM2 (Power-Up in Standby)

What does SSC do and in what cases would I want to disable it?
I am guessing that option 2 keeps the harddrive on and spinning while the computer is in standby. Is there any reason that I would want that?

 

[BillR]

Have you gone to WD’s web site and looked at the instructions?

 

[MirrorIK]

You make things too easy.

And for people who want to know;

Description of Spread Spectrum Clocking:

Computer electronics utilize “clocks” that alternate electricity to synchronize bits of data as they move from one circuit in a device to another. Similar to radio waves, these “clocks” have a certain frequency of energy radiated that can interfere with another device in the vicinity. This radiation is referred to as electromagnetic interference, or EMI.

The Federal Communications Commission (FCC) regulates broadcast emissions, such as radio and TV, as well as EMI emissions that may interfere with them. Computer and other electronic devices must meet certain requirements to limit the level of EMI they radiate. The design of a device must be changed to meet these requirements or be in violation of FCC regulations. The concept of spread-spectrum clocking is gaining popularity as a simple way to lower EMI, which is becoming more severe as processors and their “clocks” increase in speed. This method is an alternative to major design changes, which may be costly and require limiting the performance of a device. Spread-spectrum clocking speeds up and slows down the clock within a few percent of its target frequency, thus flattening out the EMI peak by spreading it across a range of frequencies.

Fluctuating the clocking speed must be tolerated by other circuits and devices involved, otherwise the devices lose their synchronization and may not communicate properly. As long as the devices are synchronized, they will communicate properly without it being necessary to lower the clocking frequency, which in turn lowers performance.

The effect of Spread Spectrum Clocking on drive/computer performance:

Spread-spectrum clocking does nothing more than help a device lower its emissions to meet FCC regulations. A computer may not need spread-spectrum clocking enabled to pass FCC regulations. Having spread spectrum clocking enabled does not affect performance. However, it requires that other devices involved tolerate fluctuating the clocking. If your Serial ATA controller or controller card do not support SSC, you should leave the jumper shunt on your WD Serial ATA drive in the SSC disabled position.

and

Power management allows the drive to be powered-up into the Standby power management state to minimize inrush current at power-up and to allow the host to sequence the spin-up of devices.

All Western Digital Serial ATA hard drives come with PM2 (power management) disabled. This setting should be used for desktop/workstation computers. If you are using the drive in a RAID/enterprise environment, and wish to enable power management on the drive (controlled spinup via spinup command per ATA standard), place a jumper shunt on pins 3 and 4.

Note: Pins 5-8 are for factory use only and should not be used by end-users.

And one question that I could not find information for on WD's site; Is there a difference between the Raptors with the jumper information and the ones without? I know they both exist.