The hard drives may fall back to the legacy PIO (Programmed
Input/Output) access mode. PIO mode is fairly slow and imposes an
excessive processor load. Evident symptoms include
- Overall performance low.
- System response "jerky", even for a simplistic tasks.
- Video playback is not possible (frame rates low, down to less
than one frame per second in extreme cases)
To verify the drive mode,
- Open the Device Manager (right click "My Computer", select
"Manage", then navigate to "Device Manager").
- On the right-hand panel, double click "Primary IDE channel"
under "IDE ATA/ATAPI controllers".
- In the window appeared, switch to the "Advanced Settings" tab.
This yields a window similar to the screenshot below.
- Make sure "Transfer Mode" is set to "DMA if available" on both
devices.
- "Current Transfer Mode" should read "Ultra DMA Mode X" for all
the installed devices. Hard drives are typically running in UDMA 4
or UDMA 5, CD and DVD drives typically use UDMA 2.
- Repeat steps 2-5 for the "Secondary IDE channel" if available.

IDE drives in PIO mode
"PIO Mode" readout (as illustrated above) indicates
that drives cannot reliably communicate with the controller using DMA
modes. The system detects communication problem and degrades drives to
PIO mode.