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Date:	Sun, 4 Apr 2010 13:33:09 +0800
From:	tek-life <>
Subject: Fwd: Can we remove the Zone_DMA?

Thanks for your reply.And do you means that , If I use a modern PC,such as
my pc (CPU:Intel dual-core 2.6GHZ; Memory 2GB; And no pci ).I can remove the
ZONE_DMA .And make sure this system also run smoothly as before?

在 2010年4月4日 下午1:07,Daniel Hazelton <>写道:

On Sunday 04 April 2010 12:21:54 am tek-life wrote:
> > I’m a newbie on the linux kernel. Now I am reading the source code of
> > Linux . I have a question in the following about ZONE_DMA.
> >
> >
> > In Linux , The Memory is divided to three zone. They are ZONE_DMA
> > 、ZONE_NORMAL  and ZONE_HIGHMEM. From the book of "Undstand the Linux
> > kernel ", the ZONE_DMA has the effect that the Direct Memory Access
> > (DMA) processors for old ISA buses have a strong limitation: they are
> > able to address only the first 16 MB of RAM. SO ,we must set a zone
> > for  the DMA on ISA bus.  And I suspect that the hardware has
> > developed so quickly .And  in this days the ISA has been weeded out.
> > And so ,if we not defined the ZONE_DMA, is the system be effected? And
> > why not remove ZONE_DMA from the kernel . If it cann‘t to do so,the
> > compatibility is the only reason?
> While ISA is gone as a true peripheral interconnect for new systems it
> does,
> actually, still live on in a lot of systems that Linux still supports.
> While
> those systems, generally, are running the same kernel and userspace they
> were
> a decade ago I have no doubt that somebody might find an old machine and
> put
> Linux on it - just because they could.
> And that also discounts the non-IBM PC machines that are out there that
> Linux
> also supports. While I don't know enough about them to say for sure, I am
> quite certain that at least some of them are still using the ISA bus.

Laboratory of Service Computing Technology and System


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