Maximum RAM on 64-bit

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So Call Me Crazy

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

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

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

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

Stef
 
Stefan said:
Technically, yes. But only about 3.2 is available to the user. The
balance is reserved exclusively for the System.
Click to expand...

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.
 
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.
Click to expand...

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
 
Stefan said:
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
Click to expand...

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
 
Stefan said:
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."
Click to expand...

I've seen anywhere from 2.7 to 3.7 available out of 4 GB. and it is the
memory addresses that are being used not the memory itself. Give it
up, you're clutching at straws.
 
Bob I said:
128 GB on XP-64 but 32-bit has 4 GB of address space, not 3.
Click to expand...

Yes, but that 4GB space is used to access video RAM, BIOS, and a few
other things besides system RAM.
 
Yep, that dead horse has been tenderized

Tim said:
Yes, but that 4GB space is used to access video RAM, BIOS, and a few
other things besides system RAM.
Click to expand...

Yep, that dead horse has been tenderized
 
I've seen anywhere from 2.7 to 3.7 available out of 4 GB. and it is the
memory addresses that are being used not the memory itself. Give it
up, you're clutching at straws.
Click to expand...

Based on Paul's explanation making a distinction between "reserved" and
"inaccessible," it seems the word "reserved" has special meaning to those
who's vocation are computers other than how it is general used.

Stef
 
Stefan said:
Based on Paul's explanation making a distinction between "reserved" and
"inaccessible," it seems the word "reserved" has special meaning to those
who's vocation are computers other than how it is general used.

Stef
Click to expand...

It does. "Reserved" means the function is not documented. It may not
rule out absolutely, the ability to access the thing. You may still be
able to read or write a Reserved location.

"Inaccessible" is more absolute, in that any attempt to use the resource
will be repulsed by force (bus fault handler etc.). In this specific case,
the problem is, there is no architectural connection, between some 800MB
of memory locations, and the address bus on the processor. No 32 bit addresses
sent by the processor, can get to those memory locations.

If the processor is set up to use 36 bit addresses (i.e. PAE),
then those locations could be accessed. They'd no longer be
inaccessible, due to a decoding limitation.

Compare these two chip specifications.

Address 0x08 Reserved
Address 0x04 Master_Reset
Address 0x00 Device_ID

versus this one

Address 0x04 Master_Reset
Address 0x00 Device_ID

If I probe location 0x08 on the second chip, I get a bus fault ("Inaccessible").
If I probe location 0x08 on the first chip, I get data, but I don't
know what it does.

I may be able to write to location 0x08 on the first chip, but since
I don't know what the location does, the chip may go nuts as a result
of me playing around. Engineers at the motherboard companies, spend
part of their day, doing exactly that, to discover functions that
Intel does not document. In that context, Reserved means "we're not
telling you what this does" and it also means "we reserve the
right to change what this register does, in any new revision of
chip we release". The register may still happen to work, but
only a fool would depend on it for some function. Some BIOS are
written to access Reserved locations, at the peril of a new
chip revision failing to work properly as a result. It means if the
chip revision is changed, the motherboard design team has to
re-test their hardware design again, for collateral damage.
So fooling around with a Reserved resource, wastes engineering
resources.

Paul
 
If the processor is set up to use 36 bit addresses (i.e. PAE),
then those locations could be accessed. They'd no longer be
inaccessible, due to a decoding limitation.
Click to expand...

Even PAE cannot solve it alone. Memory locations must be remapped. The
overlap between MMIO and DRAM is usually solved by moving the overlapped
DRAM up above 4G. PAE can then be used to get to it.
 
Stefan said:
Based on Paul's explanation making a distinction between "reserved" and
"inaccessible," it seems the word "reserved" has special meaning to those
who's vocation are computers other than how it is general used.
Click to expand...

Have you ever seen a "Reserved" Sign? It means "set aside" just in case
something "might need it". Memory addresses are assigned to hardware,
they are being used, not "reserved", whether that hardware is a video
card, USB port or RAM. Everybody just seems to get into a regular tizzy
about the RAM assignments though.
 
Have you ever seen a "Reserved" Sign? It means "set aside" just in case
something "might need it". Memory addresses are assigned to hardware,
they are being used, not "reserved", whether that hardware is a video
card, USB port or RAM. Everybody just seems to get into a regular tizzy
about the RAM assignments though.
Click to expand...

It really depends on how you use the word "reserved" and in what context.

To say that a part of the address space is reserved for other use than
DRAM is very valid.
 
dennis said:
It really depends on how you use the word "reserved" and in what context.

To say that a part of the address space is reserved for other use than
DRAM is very valid.
Click to expand...

Since those addresses aare already in use addressing the hardware, it is
somewhat difficult to say they are "reserved" for other use?
 
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