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From:	Martin Str|mberg <ams AT speedy DOT ludd DOT ltu DOT se>
Subject:	Re: Problems with timer interrupt chaining and SmartDrv
Newsgroups:	comp.os.msdos.djgpp
References:	<001701c4e2f2$e397dcc0$e1b92951 AT josepmariaxp> <01c4e32a$Blat.v2.2.2$fb750ba0 AT zahav DOT net DOT il> <20041216081608 DOT GA17913 AT webhome DOT cz> <01c4e368$Blat.v2.2.2$592f6a00 AT zahav DOT net DOT il>
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Date:	18 Dec 2004 11:09:24 GMT
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Eli Zaretskii <eliz AT gnu DOT org> wrote:
> It sounds like you are assuming that DMA is faster than PIO.  That was
> so once, long ago, mainly with floppy drives, but is no longer true
> since ATA interfaces conquered the PC land.  Nowadays, PIO is faster
> than DMA, so AFAIK DMA is no longer used in disk I/O.

For DOS maybe, not for a multitasking system.

> Also, DMA in the PC design has a disadvantage in that it completely
> takes over the bus, which means that no other activity can go on if it
> needs to talk to some other peripheral card.

You're right with regards to ISA DMA. But I think you're wrong when it
comes to PCI DMA. But I'm not an expert in this field.

I also think the name (Ultra) DMA really means something and isn't
something that the PR department is touting.

> Finally, I think BIOS is used even on Windows and Linux, so DOS is not
> the only OS they need to think about.

In Linux the BIOS is only used for booting. When the kernel has taken
over it talks direct to the hardware.


Right,

						MartinS

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