Why are there two Primary channels?
Because each IDE controller can handle two channels (two sockets on the cable) master and slave
Are they conflicting and keeping the second DVD in PIO mode despite the 'request' for DMA if available?
No but now it gets complicated :0)
Re-enable DMA using the Registry Editor
Run REGEDIT. Go to the following key:
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. Check the DriverDesc value to see which one it is.
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).
DMA Reset Tool http://svp.co.uk/helpdesk/index.php?m=downloads&a=viewdownload&downloaditemid=15 will do it for you.
Alternative Method—Uninstalling the Port 1. Uninstall the secondary IDE port To do that, open Device Manager as follows. Right-click on My Computer, select Properties, click on the Hardware tag, click on the Device Manager button, click on the plus sign to the left of IDE ATA/ATAPI Controller, right-click on Secondary IDE Channel, click on Uninstall. Deactivating is not enough.
Reboot to make the changes active and permanent.
After booting Windows will automatically reinstall the IDE channel and the DVD (or CD) drive. This Plug-n-Play process can take a little while, so give it a minute after the boot process finishes.
- Reactivate DMA But this is not enough, because unfortunately Windows does not automatically activate DMA on a DVD or CD drive. You have to tell Windows to try to use DMA first.
For that, go to Device Manager again. Right-click on My Computer, select Properties, click on the Hardware tag, click on the Device Manager button, click on the plus sign to the left of IDE ATA/ATAPI Controller, double-click on the secondary IDE channel, click on Extended Settings and change the relevant setting from PIO only to DMA when available.
On Windows NT and 2000 you now have to reboot a second time, but Windows XP applies the change instantly. Then you can go to the same place in Device Manager again and check whether the device is now actually using DMA mode. If so, all is well.
- Driver is not intended for this platform If you keep getting the following error message:
There is a problem installing this hardware.
An error occurred during the installation of the device. Driver is not intended for this platform.
then the way out is to rename C:\WINDOWS\system32\drivers\atapi.sys (or a similar path on your computer) to something like atapi.old.
If that's not possible, you can try it from the repair console (boot from the Windows install CD and select the repair console).
If Windows always automatically recreates atapi.sys, you can try renaming it in safe mode or from a command line window or you can try to rename or remove it in the driver cache as well.
Desensitize Your Computer's IDE Channels There's a bit more to it. The following article offers a way to reduce the incidence of this problem, although it still doesn't solve it altogether.
IDE ATA and ATAPI Disks Use PIO Mode After Multiple Time-Out or CRC Errors Occur http://support.microsoft.com/?kbid=817472
Do read this article because it contains a useful long-term workaround. But you have to go through the procedure described here to re-enable DMA first. Assuming you've done that, insert the ResetErrorCountersOnSuccess registry values mentioned in this article into both the primary and the secondary IDE port registry keys as described.
Unfortunately this is only a half solution, because when you enter an unreadable DVD, you will get 6 errors in a row, and the IDE channel will revert to PIO mode, but at least when you pull out the DVD in time and then insert a good one, the error counter will be reset and it will at least be a bit more difficult for Windows to hobble your IDE drive.