More than 3GB with 32-bit OS


P

Pimpom

I've long heard that a 32-bit OS can use only up to 3.25 GB
system memory. This is the case with my own computer which has 4
GB installed and TaskManager shows 3.25GB usable memory. However,
while checking around for a new system, I read in some Asus
motherboard manuals that if 4GB or more is installed, a 32-bit
Windows OS may recognize less than 3 GB and they recommend
installing a maximum of 3 GB.

The usable memory size obviously does not drop below 3GB in all
installations of 4GB and 32-bit Windows. So why the heads up from
Asus? Can it happen under certain combinations of hardware and/or
software?
 
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P

Pimpom

Grinder said:
32-bit operating systems, with some sort of Physical Address
Extension
(PAE), will never be able to fully utilize 4GB. Windows XP, by
default does not use PAE. It does look like you can enable it:

http://msdn.microsoft.com/en-us/windows/hardware/gg487503

...but my understanding it is not supported nor recommended by
Microsoft.

Actually my question was not about being able to use 4GB, but
about the possibility of being reduced to less than 3 (three) GB
if 4GB or more is installed. That possibility is clearly stated
by Asus in their manuals. I've just found the manual again.
Here's a direct quote:

"When you install a total memory capacity of 4GB or more, Windows
32-bit operating system may only recognize less than 3GB. We
recommend a maximum of 3GB system memory if you are using a
32-bit Windows operating system."
 
J

John McGaw

Actually my question was not about being able to use 4GB, but
about the possibility of being reduced to less than 3 (three) GB
if 4GB or more is installed. That possibility is clearly stated
by Asus in their manuals. I've just found the manual again.
Here's a direct quote:

"When you install a total memory capacity of 4GB or more, Windows
32-bit operating system may only recognize less than 3GB. We
recommend a maximum of 3GB system memory if you are using a
32-bit Windows operating system."
4gB is the upper limit of RAM addressability in a 32-bit OS -- there aren't
enough address lines to do any more. The reason that a given system might
(will) be able to access less as general purpose RAM is that addresses are
used up for other things. In a modern system the biggest culprit is the
display controller. Have a video card with 512kB? Then that 512kB is
subtracted from your RAM. Have a golly gee wiz 1gB card? Then that 1gB is
subtracted. There are little bits of memory besides the video card and
there always have been but modern video cards aimed at gaming have so much
memory that the situation has gotten much worse quite suddenly.

These may clarify:

http://www.zdnet.com/blog/hardware/clearing-up-the-3264-bit-memory-limit-confusion/3124

http://www.dansdata.com/askdan00015.htm
 
D

Darklight

John said:
4gB is the upper limit of RAM addressability in a 32-bit OS -- there
aren't enough address lines to do any more. The reason that a given system
might (will) be able to access less as general purpose RAM is that
addresses are used up for other things. In a modern system the biggest
culprit is the display controller. Have a video card with 512kB? Then that
512kB is subtracted from your RAM. Have a golly gee wiz 1gB card? Then
that 1gB is subtracted. There are little bits of memory besides the video
card and there always have been but modern video cards aimed at gaming
have so much memory that the situation has gotten much worse quite
suddenly.

These may clarify:

http://www.zdnet.com/blog/hardware/clearing-up-the-3264-bit-memory-limit- confusion/3124

http://www.dansdata.com/askdan00015.htm

just for a heads up i just done an upgrade to asus m4a77t/usb3 motherboard
i could not install windows xp. i could install vista.

the winxp install when it tried to reboot after copying the instalation
files gave me some error about incorrect partition.
 
D

Darklight

Darklight said:
just for a heads up i just done an upgrade to asus m4a77t/usb3 motherboard
i could not install windows xp. i could install vista.

the winxp install when it tried to reboot after copying the instalation
files gave me some error about incorrect partition.


Owe i forgot to say i had some one ask me to reinstall their laptop
it had vista on it tried to install win xp again no go.
 
P

Paul

Grinder said:
Yeah, sorry, sort of skimmed your message. Sorry about that.

1) The 4GB limit, is a "RAM license" limit.
2) The later service packs of WinXP x32, come with PAE enabled.
PAE must be enabled, to support the NoExecute (NX) feature.
PAE is not being enabled from a customer-centric viewpoint, to
enable large memory usage. It's for NX instead.
(It allows marking pages as not executable.)
3) As proof of this, try installing this RAMdisk.

http://memory.dataram.com/products-and-services/software/ramdisk

This RAMDisk wouldn't be able to access memory above 4GB,
unless a PAE page table setup was in place.

The experiment I've done is:

1) Install 6GB of memory on P5E Deluxe.
2) Operating system used is WinXP Pro x32 SP3.
PAE is enabled by the OS (I didn't need to modify boot.ini).
3) When configuring the RAMDisk, it would install a 2GB
RAMDisk (using memory above 4GB). This can't be
accessed without PAE, as far as I know. And that
memory can't be used by programs. The reason the
RAMDisk can do it, is the RAMDisk lives in "driver land"
and the rules there differ.

The result of my experiment is, "3GB available" in the OS
itself, 2GB used by the RAMDisk, and 1GB remains inaccessible.

That means, my x32 computer was using *5GB* of RAM during the test
which lasted four days.

Even though the missing 1GB is probably lifted above the 4GB
mark, the RAMDisk won't use it.

Benchmarking the 2GB RAMDisk, is shown in this picture. I
wish I'd kept a picture of Task Manager, with everything
showing.

http://img196.imageshack.us/img196/8694/hdtunedataram2gbabove.gif

Background info:

http://en.wikipedia.org/wiki/Physical_Address_Extension
http://en.wikipedia.org/wiki/3_GB_barrier

The memory license is for physical memory, and if you have
a swap file, then more than 4GB worth of programs can be
loaded. As long as the larger programs aren't resident, you
might still have some performance.

As a further experiment, I used the 2GB RAMDisk as a swap
file for the 3GB OS, and it was as smooth as silk, when
filled past the usual 3GB limit. The only problem is,
while that RAMDisk program is good, it still isn't
bulletproof. I no longer use that configuration,
because of detected anomalies (two problems in
four days testing). But if you wish to use that
RAMDisk for ordinary storage, it seems to be a lot
better than the last time I tested it. It crashed
pretty well immediately, the first time I ran it.
The recent versions are much better. Whoever wrote
that thing, knows a lot.

Paul
 
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N

news.kpn.nl

Pimpop

A 32 bit OS has a max address space of 4GB (to be precise 2^32=
4,294,967,296 )
Also the system itself needs part of this address space
For example if you have a video card with 1 GB of RAM then together with
address space need of other system hardware, only a maximum of about 2.8 GB
of adress space is left for your RAM

See you, Jan
 
P

Pimpom

John said:
4gB is the upper limit of RAM addressability in a 32-bit OS --
there
aren't enough address lines to do any more. The reason that a
given
system might (will) be able to access less as general purpose
RAM is
that addresses are used up for other things. In a modern system
the
biggest culprit is the display controller. Have a video card
with
512kB? Then that 512kB is subtracted from your RAM. Have a
golly gee
wiz 1gB card? Then that 1gB is subtracted. There are little
bits of
memory besides the video card and there always have been but
modern
video cards aimed at gaming have so much memory that the
situation
has gotten much worse quite suddenly.
These may clarify:

http://www.zdnet.com/blog/hardware/clearing-up-the-3264-bit-memory-limit-confusion/3124

http://www.dansdata.com/askdan00015.htm

I haven't had time to read through everything in detail yet, but
a quick first glance, particularly at the second link, was very
helpful. I'll go through it in more detail later. Thanks.
 
P

Pimpom

Paul said:
1) The 4GB limit, is a "RAM license" limit.
2) The later service packs of WinXP x32, come with PAE enabled.
PAE must be enabled, to support the NoExecute (NX) feature.
PAE is not being enabled from a customer-centric viewpoint,
to
enable large memory usage. It's for NX instead.
(It allows marking pages as not executable.)
3) As proof of this, try installing this RAMdisk.


http://memory.dataram.com/products-and-services/software/ramdisk

This RAMDisk wouldn't be able to access memory above 4GB,
unless a PAE page table setup was in place.

The experiment I've done is:

1) Install 6GB of memory on P5E Deluxe.
2) Operating system used is WinXP Pro x32 SP3.
PAE is enabled by the OS (I didn't need to modify boot.ini).
3) When configuring the RAMDisk, it would install a 2GB
RAMDisk (using memory above 4GB). This can't be
accessed without PAE, as far as I know. And that
memory can't be used by programs. The reason the
RAMDisk can do it, is the RAMDisk lives in "driver land"
and the rules there differ.

The result of my experiment is, "3GB available" in the OS
itself, 2GB used by the RAMDisk, and 1GB remains inaccessible.

That means, my x32 computer was using *5GB* of RAM during the
test
which lasted four days.

Even though the missing 1GB is probably lifted above the 4GB
mark, the RAMDisk won't use it.

Benchmarking the 2GB RAMDisk, is shown in this picture. I
wish I'd kept a picture of Task Manager, with everything
showing.

http://img196.imageshack.us/img196/8694/hdtunedataram2gbabove.gif

Background info:

http://en.wikipedia.org/wiki/Physical_Address_Extension
http://en.wikipedia.org/wiki/3_GB_barrier

The memory license is for physical memory, and if you have
a swap file, then more than 4GB worth of programs can be
loaded. As long as the larger programs aren't resident, you
might still have some performance.

As a further experiment, I used the 2GB RAMDisk as a swap
file for the 3GB OS, and it was as smooth as silk, when
filled past the usual 3GB limit. The only problem is,
while that RAMDisk program is good, it still isn't
bulletproof. I no longer use that configuration,
because of detected anomalies (two problems in
four days testing). But if you wish to use that
RAMDisk for ordinary storage, it seems to be a lot
better than the last time I tested it. It crashed
pretty well immediately, the first time I ran it.
The recent versions are much better. Whoever wrote
that thing, knows a lot.
Ah, RAM disk. One of many things I miss about Amigas. RAM Disk
came integrated into the Amiga OS and I used it regularly. It was
utterly stable, size was dynamic and used whatever portion of
physical memory was unused by other processes.

Your experiments with large RAM amounts are interesting and I'll
definitely try them out when I get my new system.
 
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P

Pimpom

Grinder said:
Yeah, sorry, sort of skimmed your message. Sorry about that.

No problem. What I hate is when someone misses the point of a
carefully worded post and when it's pointed out, responds with
bluster and lame excuses.
 

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