Charles Randall wrote:
>
> From: Terry Lambert [mailto:[EMAIL PROTECTED]]
> >I have yet to see one person using it for anything. So far,
> >it is nothing more than marketing fodder: I haven't seen one
> >motherboard capable of more than 4G worth of SIMMs.
>
> The Dell PowerEdge 6450 supports 8 GB of RAM.
>
> http://www.dell.com/us/en/biz/products/model_pedge_pedge_6400.htm
>
> If I understand your comments in a few follow-up messages
> correctly you're saying that this effort may be better spent
> by working on an IA-64 port and making it support large memory
> configurations?
The IA64 intrinsically supports a physical address space of 2^64,
so an address space of 2^36 vs. 2^32 is spectacularly unimpressive.
> Can you elaborate?
Yeah, the overhead in doing this will up the CPU utilization
to the point where it becomes fairly useless to do the swapping
to and from above 4G, vs. just swapping normally.
The costs involved in doing DMA to/from the memory region
above 4G will be incredible, unless the address space is
both exported, and known, to the PCI bus; even then, it
could only work for 64 bit cards, since 32 bith cards will
only be able to address the first 4G of physical memory.
I can think of one or two uses for the memory, assuming
the ability to DMA into and out of it with a 64 bit card,
and the ability to shove a 1G or 2G window around in it
so the kernel can get at the memory when it needs to, but
the overhead seems to me to be high enough that you are
better off buying a Sibytes card, running NetBSD on the
MIPS processors on the thing, plugging in 16G of RAM, and
calling your PC a "control processor".
-- Terry
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