Well, there's good news and there's bad news. The good news is that a UDMA controller can be used with both UDMA hard drives and legacy EIDE hard drives, and will be a lot faster than an EIDE controller. The bad news is that they're not technically supported by the current stable releases of Linux (2.0.x kernels). In some cases the controllers can be used in legacy (EIDE-compatible mode) with no difficulty, in others simply using the controller requires a bit of effort. In all cases, in order to use UDMA transfer speeds, an appropriate patch is required. The following sections will each pertain to a specific type of UDMA controller.