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From: Stefan Patric on 2 Jun 2010 16:57
On Wed, 02 Jun 2010 09:17:07 -0700, So Call Me Crazy wrote:

> What is the maximum RAM XP 64-bit will utilize? I know it's 3 GB on
> 32-bit, but...

Be aware that max addressable RAM is limited by hardware, too. That is,
how much can be installed and recognized. For example, was upgrading a
friend's old (10 years, at least) HP desktop with Windows ME on it to a
more suitable OS. It had 2 RAM slots with one 128MB chip installed. The
specs from HP said max RAM was 512MB (2 x 256MB) even though 32-bit can
address 4GB. I put two old, but tested and working, 512MB compatible
DIMMs in it for 1GB, but only 512 of it was recognized by the hardware.
(Probably a BIOS limitation, but it had the latest BIOS available.) So,
I put two 256MB chips in it, and it recognized 512MB. 512MB was a
hardware limitation not an OS one.

Just so you know...

Stef
From: Stefan Patric on 2 Jun 2010 22:23
On Wed, 02 Jun 2010 13:51:37 -0500, Bob I wrote:

> 128 GB on XP-64 but 32-bit has 4 GB of address space, not 3.

Technically, yes. But only about 3.2 is available to the user. The
balance is reserved exclusively for the System.

Stef

> So Call Me Crazy wrote:
>
>> What is the maximum RAM XP 64-bit will utilize? I know it's 3 GB on
>> 32-bit, but...
>>
>> TIA
>>

From: Bob I on 3 Jun 2010 08:39


Stefan Patric wrote:

> On Wed, 02 Jun 2010 13:51:37 -0500, Bob I wrote:
>
>
>>128 GB on XP-64 but 32-bit has 4 GB of address space, not 3.
>
>
> Technically, yes. But only about 3.2 is available to the user. The
> balance is reserved exclusively for the System.
>

The variable amount of unused RAM is entirely dependant on the
particular hardware installed on the particular computer. The OP stated
that 3 GB was the limit and that is incorrect. As to 3.2 GB, once again
that is NOT a limit, nor is it "reserved", it is used to comunicate with
installed hardware. Remove or reconfigure hardware and the value will
change. All you can say is that 3.2 GB is an approximate value for
common pc configurations.

From: Stefan Patric on 3 Jun 2010 17:42
On Thu, 03 Jun 2010 07:39:24 -0500, Bob I wrote:

> Stefan Patric wrote:
>
>> On Wed, 02 Jun 2010 13:51:37 -0500, Bob I wrote:
>>
>>
>>>128 GB on XP-64 but 32-bit has 4 GB of address space, not 3.
>>
>>
>> Technically, yes. But only about 3.2 is available to the user. The
>> balance is reserved exclusively for the System.
>>
>>
> The variable amount of unused RAM is entirely dependant on the
> particular hardware installed on the particular computer. The OP stated
> that 3 GB was the limit and that is incorrect. As to 3.2 GB, once again
> that is NOT a limit, nor is it "reserved", it is used to comunicate with
> installed hardware. Remove or reconfigure hardware and the value will
> change. All you can say is that 3.2 GB is an approximate value for
> common pc configurations.

And that is why I said "about 3.2" meaning not exactly 3.2, but around
3.2 or approximately 3.2. Even on a system with the barest of hardware,
I myself have never seen more than about 3.35 available. Although, I've
read claims of 3.5.

Also, what would you call RAM that is exclusively accessible ONLY by the
system for its use, that is, users or their apps can't access it? To me,
that is the very definition of "reserved."

Stef
From: Paul on 3 Jun 2010 18:09
Stefan Patric wrote:

>
> Also, what would you call RAM that is exclusively accessible ONLY by the
> system for its use, that is, users or their apps can't access it? To me,
> that is the very definition of "reserved."
>
> Stef

That is not "reserved", it is "inaccessible" memory, since
no mapping in the chipset decoders makes it possible to
get to the memory locations in question. And I'm referring to
processor access. When the processor sends an address over the
FSB, the chipset maps the address to the appropriate piece of
hardware. And in this case, where Windows indicates ~3.2GB
free, it means 800MB of memory simple cannot be accessed from
the processor. The memory continues to be refreshed by the DRAM
controller (a function local to the Northbridge), and the
Northbridge has visibility to the RAM, but the processor can't
get there.

*******

For some interesting background on what might have been
possible, try this article. PAE makes it possible, for a 32 bit
OS to address a 36 bit or larger address space. Individual programs
cannot use all the memory at once with that scheme - it would
take multiple programs to be able to actually use all the memory,
but PAE does offer a better alternative for someone who happens
to buy too much memory for their computer. This person did some
experiments, to show how easy it is to do.

http://www.geoffchappell.com/viewer.htm?doc=notes/windows/license/memory.htm

It is possible WinXP SP1 would have allowed this also. That is addressed
in this section of that article.

"Windows XP SP2

Special mention must be made of Windows XP SP2 and SP3. If you were
fortunate enough to have 4GB in a machine for running a client version
of Windows up to and including Windows XP SP1, and your hardware had
memory remapping so that some of your 4GB was above the 4GB address,
and your third-party drivers worked correctly with memory above 4GB,
then you will have faced an unfortunate side-effect when upgrading to
Windows XP SP2: you will have bought a downgrade of how much RAM
Microsoft permits you to use."

If you wanted to use the entire 4GB, then your best bet would be
WinXP SP1, rather than SP2 or SP3. Remapping should be turned on in
the BIOS, if your BIOS doesn't automatically do the right thing.
And that is for the x32 bit version of the OS, as x64 would be
fine on its own.

HTH,
Paul
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