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SubjectRe: A question about ZONE_DMA
Date
On Wednesday 13 October 2010, Casey Dahlin wrote:
> So if I understand correctly, ZONE_DMA exists to separate and preserve the
> chunk of memory to which older ISA cards are capable of doing DMA. The question
> that arises for me is:
>
> 1) Why do all 32-bit boxes have a ZONE_DMA when surely only a tiny and
> shrinking number of them have a need for it?
>
> 2) Why do any 64-bit boxes have a ZONE_DMA? Is there really some godless
> monster out there who put an early ISA bridge and a 64-bit CPU on the same
> motherboard?!
>
> Can someone shed light on what I'm missing?

There are some ISA devices that have become standard components, like floppy
drives. A lot of PCs still have connectors for floppies even though they
are hardly used these days.

Some architectures define ZONE_DMA in a different way, e.g. as the lower
2 GB because of device restrictions on 64 bit systems.

Arnd


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