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I have a Windows XP system with 2 SATA hard drives - WD Raptor 300 & WD Caviar 500. The motherboard is P31 and I have UDMA enabled in the BIOS.

Now the Raptor works in DMA mode while the Caviar only works in PIO mode. So what are the possible reasons for that?

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up vote 2 down vote accepted

Windows defaults back to PIO mode if it encounters a succession of errors/timeouts while transferring data. The data transfer error cause can be various - faulty cables, faulty ports, interference, bad hard disk - to name a few.

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To fix this, open up the Device Manager and uninstall the hard drive. It will prompt you to reboot, then Windows will reinstall the driver with the transfer mode set to DMA (then reboot again). – Bigbio2002 Dec 4 '15 at 0:11

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