Overclocking & hard drives-
Only follow these steps if you're overclocking!
If you're an avid overclocker you probably have had some bad experiences. Most bad experiences may be caused by the ram not being able to handle the high speeds, heat, or even voltage.
But one problem that is very annoying is hard drives that do not like to be overclocked. The culprit is usually UDMA, or certain brands (in my experience, Fujitsu and IBM have been known to cause awful problems).
Running a hard drive at a higher speed requires a more precise timing. By overclocking the PCI bus you're running a risk for your hard drives. Some brands actually will lose all the data, or scramble it completely. Since this is obviously very annoying, a little tweaking is necessary.
First you must understand why these problems occur.
Look at the table below, demonstrating the PCI speed of 1/2 bus clock speed (remember FSB means the bus speed of your PCI would be 66 x 1/2 = 33 MHz).
Keep in mind that your PCI bus is supposed to run at 33 MHz.
No hard drives should have problems at 33 MHz, few will fail at 37 MHz, and quite a few can fail at 41/44 MHz. Enabling UDMA / bus mastering often leads to even more problems when running at these speeds, because it gets more complicated for the system. The worst things that I have seen overclocking do to hard drives can be solved by fdisk/formatting the drive.
How to prevent it-
You cannot entirely prevent it, but you can take precautions. Although no hard drive really works 100% of the time at these speeds, usually the best hard drives for these speeds are Seagate, Western Digital, and Quantum.
Some motherboards like the ABit BH6 and ASUS P2B offer a 1/4 PCI speed multiplier. This is a great idea, and surely avoids all problems with overclocking & hard drives in the near future.
If you've never ran your hard drive at 37 MHz / 41 MHz / 44 MHz bus before you should take extra precaution. Back up all important data in case you happen to lose everything. It is VERY important to at first remove all UDMA / bus mastering.
The next strategy is to lower the PIO mode settings and disable UDMA in your BIOS.
Change the option Master Drive (or whatever drive, etc.) PIO Mode. Usually motherboards have it set to "Auto" as default. Set this to 4, or if you know your hard drive will encounter very bad problems set this lower. The lowest it can go is 0. This will slow the speed of the hard drive, but increase the stability and decrease the probability of a crash.
Disable any options concerning UDMA, whether they say "Auto" or "Enabled", DISABLE them all.