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PIO versus DMA
The disadvantage of DMA transfer operations is that the PC/AT hard disk
controller and later IDE, evolved around PIO data transfers. Therefore, the
system Int 13h BIOS and the embedded operating system device drivers have
supported PIO transfers versus DMA transfers. This simply means that BIOS
changes and external device drivers are necessary to achieve the
incremental performance that DMA offers.
Western Digital's Enhanced IDE program supports system manufacturers'
choice of either PIO transfers via Flow control with IORDY for Mode 3 PIO
data rates or DMA transfers (both Type B and Type F) via the development of
external DMA device drivers supporting Western Digital hard disk drives.
Product platforms based on both high speed transfer options will be in
production in calendar fourth quarter 1993.
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