

No.  The simple $25 style IDE controller does not use DMA.  The CPU performs
the data transfer with a string move instruction.  This requires that the
CPU stop what it had been doing and transfer the data.  Only the smart drive
controllers, be they IDE or SCSI, can transfer via DMA.  These controllers
tend to cost the same wether they are IDE or SCSI.  To get the DMA benefits,
IDE must sacrifice it's price advantage *on the controller*.



Floppies aren't on the IDE bus, your arguement makes no sense, this isn't
an IDE issue.  The floppys have their own processor on their controller
board which handles all of these commands.

The difference between IDE and SCSI is that all SCSI peripherials are
intelligent.  They each have their own controller.  They depend on the
CPU to do fewer things for them, i.e. IDE drives needing a processor
to transfer their data.




The dettach/callback mechanism alows the CPU to make requests of the 
devices on the SCSI bus and then dettach and go about its business.
Later, when the device is done, it issues a callback to say that the
data has arrived or the function has completed.  Most SCSI cards will
also DMA the data into memory without the interupting the CPU, therefore
allowing it to continue working uninterupted.  IDE supports no such concept
as dettach/callback.  

Can you see how this would be a win in any multitasking system?

--David Willmore

-- 
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willmore@iastate.edu | "Death before dishonor" | "Better dead than greek" | 
David Willmore  | "Ever noticed how much they look like orchids? Lovely!" | 