[Info-vax] Comparison between Nehalem-EX and Power7

[Michael S]

On Sep 9, 1:49 pm, John Wallace <johnwalla... at yahoo.co.uk> wrote:
> On Sep 9, 4:28 am, Neil Rieck <n.ri... at sympatico.ca> wrote:
>
>
> Meanwhile, on a related note, what's the maximum physical memory on
> these boxes these days? Is it different between Itanium boxes and
> x86-64 boxes, and are the differences architectural (inherent in the
> chip, maybe) or just related to the number of memory slots on a
> motherboard?

Obviously, a new 800-seies platform is not for those looking for max.
memory capacity. If you are lucky with motherboard you will be able to
run 4 DIMMs at 1333 MT/s. If you are less lucky the second pair of
DIMMs will get you down to 1066 MT/s.
If you need more take older more expensive 900 series (6 DIMMs).
If you need more yet, then your only option in Nehalemland is dual
Xeon 5500 series which on some motherboards supports up to 18x8 GB
DIMMs = 144 GB.
As to architectural limitations, all desktop Nehalem variants are
limited to 36-bit physical address space.
Xeon 5500 series - 40-bit physical address space.
Incoming Nehalem EX - not known yet, most likely 44 bits.
Itanium - 50 bits

In general, current incarnation of x86-64 instruction set architecture
(a.k.a. AMD64,  a.k.a. Intel 64) is limited to 48-bit _virtual_
address space. That's probably would suffice for a couple of
decades.Going beyond that would require some, hopefully relatively
small, changes to system-layer architecture - may be a new page table
format. User-layer stuff shouldn't be affected.