The mode that Windows is using to access your hard drive and other IDE devices (CD/DVD Drives) is configured in the Windows XP Registry. My experience is that when XP detects too many errors on one of the drives (Hard Drive or CD/DVD Drive) while in DMA (fast) mode, Windows lowers it's access setting to the slower, more reliable PIO mode.
If you want to FORCE Windows to switch back to DMA mode, you can save the Registry Keys/Hives in their "DMA Mode" state to a .REG file using REGEDIT. Save this file to your Desktop (or wherever you'd like), then when you PC reverts back to PIO mode, simply LAUNCH that .REG file that contains the correct entries for DMA mode. You'll need to reboot after you import those keys - then XP should be running in DMA mode.
It's kind of a "duct-tape" fix - as the REAL fix would be to resolve the problem that's causing XP's hard drive access to keep reverting back to PIO mode in the first place.
I found very helpful, detailed documentation of this issue at the following address:http://winhlp.com/node/10
This site has much more involved and helpful information about solving this issue than the previous MS Knowledgebase post
that I referred you to in an early post. It gives specific instructions for "desensitizing" the registry settings such that XP will not be so quick to switch from DMA to PIO in the case of errors.
Hope all of this helps.
- John Hook