Windows XP: DMA Reverts To PIO After Multiple Disk Errors

Windows XP normally assigns the highest mode of operation for an IDE HDD. It them aggregates the number of CRC errors that occur on a disk. When the number of CRC errors reach 6 it downgrades the usual UDMA 5 to UDMA 4. When these errors happen frequently the HDD will downgrade to the lowest mode and get stuck in the PIO mode. Any device we use in this half of the century should not be working in PIO mode which has a transfer speed of about 3.33MBPS.

The CRC errors usually happen when the system resumes from the stand-by state. Usually the read requests are issued with a time-out value of 4 seconds. But when the drive resumes from stand-by it takes a little more than 4 seconds to spin-up. Hence the errors.

Symptoms:

• The applications suddenly become processor intensive. Since the DMA has been reverted every instruction has to go through the CPU and hence the problem.
• The Device manager show PIO mode and does NOT give a choice for changing to DMA. You can see which mode your HDD is operating in by viewing IDE ATA/ATAPI Controllers > Primary IDE Channel > Properties > Advanced Settings - Assuming your HDD is connected to the primary IDE channel.
• Explorer locks up or crashes frequently while moving a file.
• Desktop icons and taskbar disappear for few seconds when you try to refresh.

Quick Fix:

• Open Device manager and expand IDE ATA/ATAPI Controllers.
• Select the IDE channel your hard disk is on.
• Right click and uninstall.

This resets the driver for the IDE channel. The system will ask for a few (2 to be exact) restarts and the highest mode of operation is redetected. The HDD will now be seen to be working in UDMA 5 Mode which is the fastest with about an interface speed of 100MBPS.