Hard drives and DVD drives can work in 2 modes
DMA - Direct Memory Access
PIO - Programmed Input Output.
DMA is the fastest mode and so gives the smoothest results. If Windows detects a problem with a device such as a DVD Writer - often caused by a fault disc, it will automatically switch the writer to PIO mode. Suddenly you find that a disc is taking an age to burn something that normally takes a fraction of the time. For instance burning a 4.3 GB DVD at 4x should take about 15 minutes, if it starts taking a hour or more it is a strong likelihood that the device has been placed into PIO mode.
Once the device is in PIO mode it can stick in that mode and not revert back to DMA. The next time you come to play a DVD suddenly the Video is very choppy and seems to be struggling. You are likely to think that your device has dirty heads or is broken.
How to check if you are in DMA mode or PIO mode.
Go to Device Manager and look for IDE ATA/ATAPI Controllers.
Right click and select properties.
Use the drop down lists to select DMA Mode.
If for some reason it refuses to change and remains \"stuck\" in PIO mode then simply delete that channel
Either right click and select uninstall or simply press the [DEL] key on your keyboard. Restart your computer and windows will automatically re-install the channel.