If your PCI system uses IDE drive(s) (as opposed to SCSI, say) and
is capable of bus-master DMA operation (most Pentium PCI systems),
you will want to say Y here to reduce CPU overhead. You can then use
the "hdparm" utility to enable DMA for drives for which it was not
enabled automatically. By default, DMA is not enabled automatically
for these drives, but you can change that by saying Y to the
following question "Use DMA by default when available". You can get
the latest version of the hdparm utility from
<ftp://ibiblio.org/pub/Linux/system/hardware/>.

Read the comments at the beginning of <file:drivers/ide/ide-dma.c>
and the file Documentation/ide.txt for more information.

It is safe to say Y to this question.