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Did 486 ISA IDE controllers support DMA?
Posted: Thu Jun 05, 2014 7:16 am
by tom9876543
Hi,
Obviously the PCI IDE controllers have DMA support.
Were the old ISA IDE controllers (for 486 and lower) also capable of DMA??
It seems they did PIO only....
Re: Did 486 ISA IDE controllers support DMA?
Posted: Thu Jun 05, 2014 9:00 pm
by Brendan
Hi,
tom9876543 wrote:Obviously the PCI IDE controllers have DMA support.
Were the old ISA IDE controllers (for 486 and lower) also capable of DMA??
It seems they did PIO only....
For ancient hard disks the ISA DMA controller was used for DMA. When hard disks were very slow this was fine. When hard disks got faster the ISA DMA controllers weren't fast enough to keep up and (eventually) got replaced by "DMA built into the disk controller".
However, I'm not too sure on the exact history. There may have been a time before the ISA DMA controller was used and PIO was the only option. There may have also been a period of time where ISA DMA was no longer used but "DMA built into the disk controller" hadn't been introduced yet. Mostly, it was all obsolete junk before I got my first 80x86 machine (a quarter of a century ago).
Cheers,
Brendan