Exocore: "RedHat ships a highly tuned version of the Linux kernel which enables DMA (Direct Memory Access) or even Ultra DMA by
default for the IDE controller. DMA based transfers greatly reduces install time by providing faster file transfer speeds. DMA
also reduces CPU usage to a large extent for disk activity.
Because of the above mentioned benefits, DMA is a highly desirable feature and in most cases, the DMA enabled kernel works
like a charm.
For more on the benefits of using DMA transfers see http://www.linuxdoc.org/HOWTO/mini/Ultra-DMA.html.
However, DMA has its downside. It requires that all the components of your system are "healthy". If there is a hardware
related problem in any one of the related system components, DMA will fail to function properly."