On Tuesday 16 August 2005 7:17 am, Klaasjan Brand wrote: > On 8/15/05, Rick Wagner <wagnerric@xxxxxxxxxxxxxxxxxxxxxx> wrote: > > Hi, > > > > I have seen reference to kernel support for up to 32GB on 32 bit x86 > > platforms, with supporting hardware (some versions of Xeon?). > > Yes, the kernel can use up to 64Gb. > > > Perhaps I used the wrong search terms, but I could not locate much > > detailed information on the subject with Google. Specifically, I was > > told that the kernel could map the memory virtually, but the I/O > > sub-system could not handle physical I/O to address over 32 bits, thus > > I/O to high memory was done via bounce buffers (i.e., DMA to low memory, > > then CPU copy to high). > > I'm no hardware guru, but I believe it also has to do with devices on > the PCI bus not being able to access the high memory. > > > Can anyone point to some documentation on the large memory implementation > > I can use to confirm or refute what I was told? > > Search for "linux high memory"; first hit is quite extensive: > http://kerneltrap.org/node/2450 > > Klaasjan Thanks Klaasjan. This was very helpful. It mentions the PCI bus limitation, but I'm wondering about PCI-X and PCI-E, which I think go beyond 32 bit addresses. I'll keep digging, and see if there are more up to date articles; this one was based on 2.4, with mention of 2.6. Thanks again, --rick
