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From: dennis on 17 Mar 2010 02:48
On 17-03-2010 13:04, Bob I wrote:

> he said 32 CPU machine, not 32 bit. BIG difference
>

He said: "32 cpu machine". It was just a small comment to his little joke.

Anyways, AMD and Intel 32bit only CPUs support 64GB. Their 64bit CPUs
support way more than that in PAE mode... Why Win2003 supports 128GB
From: John John - MVP on 17 Mar 2010 11:00
dennis wrote:
> On 17-03-2010 13:04, Bob I wrote:
>
>> he said 32 CPU machine, not 32 bit. BIG difference
>>
>
> He said: "32 cpu machine". It was just a small comment to his little joke.
>
> Anyways, AMD and Intel 32bit only CPUs support 64GB. Their 64bit CPUs
> support way more than that in PAE mode... Why Win2003 supports 128GB

PAE is 36-bit wide and 2^36=64GB, but Server 2003 can use NUMA so
processors can use different memory banks allowing the operating system
to use a combined memory access up to 128GB. With SMP the operating
system can only access a maximum of 64GB.

John
From: dennis on 17 Mar 2010 12:52
On 17-03-2010 16:00, John John - MVP wrote:

> PAE is 36-bit wide and 2^36=64GB

PAE is actually implementation specific. In 64bit processors you can
address the entire physical bus through PAE (the PTE structure is the
same as in 64bit mode).
From: John John - MVP on 17 Mar 2010 14:04
dennis wrote:
> On 17-03-2010 16:00, John John - MVP wrote:
>
>> PAE is 36-bit wide and 2^36=64GB
>
> PAE is actually implementation specific. In 64bit processors you can
> address the entire physical bus through PAE (the PTE structure is the
> same as in 64bit mode).

But /PAE is only available on 32-bit operating systems and when
installed on 64-bit machines the processor operates in legacy mode to
suit the 32-bit operating system. I'm not sure if the processor makes
all the processor width available while in legacy mode? And being that
PAE is now a rather old story I have to wonder if Microsoft ever
designed PAE to access more than 64GB of RAM.

Microsoft says that PAE allows it's operating systems to use a maximum
of 64GB of RAM so I don't know how else (other than NUMA) Server 2003
x86 would be capable of using 128GB. Interesting to note that Server
2003 is the only one capable of using this much RAM, Server 2008 x86 can
only use 64GB... but then Microsoft decide a while back that Server 2008
was the end of the line for 32-bit server systems.

John
From: dennis on 17 Mar 2010 14:10
On 17-03-2010 19:04, John John - MVP wrote:

> But /PAE is only available on 32-bit operating systems and when
> installed on 64-bit machines the processor operates in legacy mode to
> suit the 32-bit operating system. I'm not sure if the processor makes
> all the processor width available while in legacy mode? And being that
> PAE is now a rather old story I have to wonder if Microsoft ever
> designed PAE to access more than 64GB of RAM.

64bit processors are also 32bit processors. There are different
addressing modes. PAE is one of them - used by 32bit OSes. 64bit/long
mode is another - which is used by 64bit OSes.
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