Bus Mastering Integrated Drive Electronics
Originally IDE devices, such as hard disk drives and CD-ROM units, are accessed using a method called PIO (Programmed I/O or Processor I/O). In this method the system processor is in charge of transfering data from the hard drive to the RAM memory.
The hard drive can be programmed to perform this transfer alone, not using the system CPU. This procedure is called bus mastering or BMIDE or DMA (Direct Memory Access). With the bus mastering enabled, the system performance is increased, since the system CPU will be free to perform other tasks.
In ordert to make the hard drive to use this method, you need to configure the operating system.
Hard drives above 16.6 MB/s can only achieve its maximum performance if the bus mastering is enabled.