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Old March 17, 2007, 11:09 AM
Join Date: Mar 2007
Location: Alberta
Posts: 263

My System Specs

Default DMA Re-Activation

DMA - Direct Memory Access

I came across a problem associated with XP Pro after running an old bench mark, Winbench99. The program pointed out the fact my DMA was not activated, I went to change it back in device manager and the options were greyed out.
Turns out XP Pro will switch from DMA to PIO mode if you get 6 timeout errors or more on your IDE ATA/ATIAPI drives, and the user cannot revert it with out a un-install and re-install of the device in question, this also includes HDD's.

There is a work around and it involves your registry. This is not my work around, I found it on a webpage for dvd's and I thought I would share it because it worked without issue for me.
If your DMA settings revert back to PIO after rebooting:

You can try tweaking the registry settings to reset the error count. Be very careful here.
Backup your registry before proceeding.

Go to the following key:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Contro l\Class\{4D36E96A-E325-11CE-BFC1-08002BE10318}
It has subkeys like 0000, 0001, 0002, etc. Normally 0001 is the primary IDE channel, 0002 the secondary, but other numbers can occur under certain circumstances. You have to go through these subkeys and check the DriverDesc value until you find the proper IDE channel.
Delete MasterIdDataChecksum or SlaveIdDataChecksum, depending on whether the device in question is attached as master or slave, but it can't actually hurt to delete both. Reboot. The drive DMA capabilities will be redetected.
Open Device Manager again and check whether the device is now actually using DMA mode. If so, congratulations, you've made it (at least until the next time Windows disables DMA)

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Old March 17, 2007, 11:27 AM
Babrbarossa's Avatar
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Join Date: Dec 2006
Location: New Brunswick
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My System Specs


Good thing to know- Anyone experiencing crackling sound or video from cd or dvd playback might want to look into this problem as a potential cause.
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