Added more RAM but not all is listed on My Computer > Properties

  • Thread starter Mark Christensen
  • Start date

M

Mark Christensen

I had a total of 2GB of RAM installed (4 x 512MB). I just installed another
2GB by removing 2 of the 512MB, so now I have 2 x 2GB and 2 x 512MB for a
total of 5GB (and yes they are installed in the correct matching pairs).

When I started up XP Pro I got the message that the memory had changed and
to hit F2 to enter setup, which I did and it confirmed 5GB is now installed.
So I continuted to load windows. I then right clicked on My Compuer >
Properties and it only lists 3.37GB.

I then went to System Info and on the Summary screen it lists:
Total Physical Memory 5,120.00 MB
Available Physical Memory 2.85 GB
Total Virtual Memory 2.00 GB
Available Virtual Memory 1.96 GB
Page File Space 5.21 GB

I added more RAM since I do a lot of graphics on this PC and wanted better
performance, but now I'm not sure if I'm using all the additional RAM I
bought. Is some of my new RAM not being used? Is there a way to get all my
RAM to be used?

Mark
 
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M

Mark Christensen

So doing some research I came across some info about a /PAE switch. I found
one post that said to:

"Open your boot.ini file (remove its Read-Only and Hidden attributes) and
delete the 3GB switch. Then add the /PAE switch. Reboot your computer. XP
will now see all 4 GB of RAM."

Is this safe to do? How do I do that?
 
M

Mark Christensen

Sys Info screen says my XP is Version 5.1.2600 Service Pack 2 Build 2600.
And I have a system32 folder.
 
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J

John John

No, that switch won't do that with Windows XP, it will only work with
Server versions. Furthermore, whoever wrote that post didn't know what
they were talking about, the /3GB switch deals with Virtual Address
Space available to applications, it doesn't have anything to do with
Physical Memory (RAM).

Perhaps SP3 will change that (/PAE) but I don't know, I haven't heard
reports of any changes to the XP PAE kernel with SP3 so I kind of doubt
that it will be changed to allow for use of RAM above the 4GB barrier.

You will need to use a 64-bit workstation to use all that RAM, or one of
the 32-bit 2003 Server version.

John
 
M

Mark Christensen

So is all the RAM above the 3.37 listed on the my computer > properties
wasted?

Is there any way to at least have the my computer > properties show 4GB?

Thanks.
 
J

Jim

Mark Christensen said:
I had a total of 2GB of RAM installed (4 x 512MB). I just installed another
2GB by removing 2 of the 512MB, so now I have 2 x 2GB and 2 x 512MB for a
total of 5GB (and yes they are installed in the correct matching pairs).

When I started up XP Pro I got the message that the memory had changed and
to hit F2 to enter setup, which I did and it confirmed 5GB is now
installed. So I continuted to load windows. I then right clicked on My
Compuer > Properties and it only lists 3.37GB.

I then went to System Info and on the Summary screen it lists:
Total Physical Memory 5,120.00 MB
Available Physical Memory 2.85 GB
Total Virtual Memory 2.00 GB
Available Virtual Memory 1.96 GB
Page File Space 5.21 GB

I added more RAM since I do a lot of graphics on this PC and wanted better
performance, but now I'm not sure if I'm using all the additional RAM I
bought. Is some of my new RAM not being used? Is there a way to get all my
RAM to be used?

Mark
Windows XP uses memory mapped IO. The difference between the 4 GB that you
have installed and the 3.37 GB that is available is allocated to
IO devices. Since it is highly ill advised to have a RAM stick respond to a
message sent to an IO controller, XP turns off the RAM that overlaps
the IO controllers. Thus, no you cannot get all of the RAM to be used.

Jim
 
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J

John John

In that case you cannot run a 64-bit Windows version on the machine, you
would need an x86-64 or EMT64, or an AMD64 processor to run 64-bit
Windows. The only hope that you have of being able to use all that
memory is by using one of the server versions that can effectively use
the memory with the use of PAE. Or use a 32-bit xnix PAE operating
system... Effectively, with any 32-bit Windows workstation version the
additional RAM is useless.

John
 
J

John John

Jim said:
Windows XP uses memory mapped IO. The difference between the 4 GB that you
have installed and the 3.37 GB that is available is allocated to
IO devices. Since it is highly ill advised to have a RAM stick respond to a
message sent to an IO controller, XP turns off the RAM that overlaps
the IO controllers. Thus, no you cannot get all of the RAM to be used.

That's not exactly how it works, the BIOS places a hold on some of the
available memory address space right below the 4GB barrier to make it
available to other I/O devices, so that address space isn't available to
the RAM, it's not Windows that turns off the RAM, it just that either it
isn't available to Windows at all to start with, or, if the BIOS shifts
the unavailable addressing above the 4GB barrier, it cannot be accessed
by 32-bit operating systems without the use PAE. In effect, the BIOS
reserves some of the processor's address space below 4GB exclusively for
the devices I/O usage so the processor cannot address RAM in the
reserved I/O range. Some (many if not most) newer 32-bit processors can
shift the RAM addressing above the normal 32-bit address range with the
use of PAE 36-bit addressing, but the operating system must also be
capable of using this feature. Windows XP 32-bit cannot use this PAE
feature so it cannot use all the installed RAM.

John
 
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K

Ken Blake, MVP

I had a total of 2GB of RAM installed (4 x 512MB). I just installed another
2GB by removing 2 of the 512MB, so now I have 2 x 2GB and 2 x 512MB for a
total of 5GB (and yes they are installed in the correct matching pairs).

When I started up XP Pro I got the message that the memory had changed and
to hit F2 to enter setup, which I did and it confirmed 5GB is now installed.
So I continuted to load windows. I then right clicked on My Compuer >
Properties and it only lists 3.37GB.
Is there a way to get all my
RAM to be used?


No.

Two points:

1. First of all, all 32-bit versions of Windows (not just XP) have a
4GB address space. That's the theoretical upper limit beyond which you
can not go.

2. You can't even use the entire 4GB of address space. Even though
you have a 4GB address space, it can only use *around* 3.1GB of RAM.
That's because some of that space is used by hardware and not
available to the operating system and applications. The amount you can
use varies, depending on what hardware you have installed, but is
usually around 3.1GB.

You are actually getting a little more used than the average.

Note that the hardware is using the address *space*, not the actual
RAM itself. The rest of the RAM goes unused because there is no
address space to map it too.

I added more RAM since I do a lot of graphics on this PC and wanted better
performance,


Even if you're doing a lot of graphics, my guess is that with Windows
XP you wouldn't see any perceptible increase in performance by having
more than 3.37GB. Is it faster with 3.37GB than it was with 2GB?
 

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