Re: How to debug inside the BIOS and/or interrupt?

On Fri, 06 Jul 2007 12:18:48 GMT, NoSpam@[EMAIL PROTECTED]
 (Bob Masta)
wrote:
<snip>
>I don't recall ever dealing with hard drive DMA.  I think it wasn't
>used much under DOS because it was so slow... REP INSW
>or OUTSW were significantly faster on ISA-bus machines.
>IBM set the DMA clock to half the bus speed on the AT, since
>the DMA  chips at the time were limited to 5 MHz and the AT
>bus ran at 6 MHz.  I think the half-speed tradition was carried
>on by all the clones as well.  I don't know what the current
>state of affairs is on modern systems.  A quick Google search
>gives me the impression that hard drive DMA is an option you 
>may need to specifically enable.
>
ISTR that the original PC & XT hard drive controllers used DMA.  It
was with the AT that INSW & OUTSW were used.  And now with PCI we're
back to DMA, although I do think that it defaults to PIO unless
enabled.
-- 
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