Xp only showing 2.75 GB of ram for 4GB

[Joe]

Hi All!

I installed 4GB of ram in my XP 32 bit machine w/SP2. Windows is only
showing 2.75 GB under system properties, general.

I thought the more common amount to be shown was 3.75 GB.

Does this make sense?

Thanks for any help.
Joe

 

[neil]

I think it can vary, does your system share ram for video memory.?
Neil

 

[Joe]

I'm not sure. How can I tell?

I think it can vary, does your system share ram for video memory.?
Neil

 

[Ken Blake, MVP]

Hi All!

I installed 4GB of ram in my XP 32 bit machine w/SP2. Windows is only
showing 2.75 GB under system properties, general.

I thought the more common amount to be shown was 3.75 GB.

Does this make sense?

The amount varies, depending on your hardware. It's usually *around*
3.1GB, but can be even less that what you show.

Here's my standard post on this subject:

All 32-bit client versions of Windows (not just Vista/XP) have a 4GB
address space. That's the theoretical upper limit beyond which you can
not go.

But you can't use the entire 4GB of address space. Even though you
have a 4GB address space, you can only use *around* 3.1GB of RAM.
That's because some of that space is used by hardware and is not
available to the operating system and applications. The amount you can
use varies, depending on what hardware you have installed, but can
range from as little as 2GB to as much as 3.5GB. It's usually around
3.1GB.

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.

Why did you install that much RAM? Unless you run particularly
memory-hungry applications, even 2.75GB is *way* more than you can
make effective use of running XP.

 

[BigJim]

one way to tell is open the box and look
the other way is to see if the monitor is connected to an expansion slot

 

[neil]

Well to begin with do you have a dedicated video card or is the video from
the motherboard.?
Neil

 

[Swifty]

Here's my standard post on this subject:

All 32-bit client versions of Windows (not just Vista/XP) have a 4GB
address space. That's the theoretical upper limit beyond which you can
not go.

And some hardware (my IBM Thinkcentre M52 for example) come with a
memory chip which cannot address more than 3Gb of physical RAM even if
you plug four 1Gb DIMMs into its four slots. The only reason it has four
slots is for those people with DIMMs smaller than 1Gb.

So, having three 1Gb DIMMs plugged in, adding anything extra would make
not a jot of difference (other than heat and load on the power supply)
as it would be allocated an address which the hardward cannot reference.

The limitation, in this case is the memory controller, which I believe
is an Intel component, common across other systems as well. I find it
hard to credit that hardware would be designed which could address 3Gb
but not 4Gb (its the same number of address bits!) but someone must have
had a good reason, or a bad day at the drawing board.

 

[Ken Blake, MVP]

And some hardware (my IBM Thinkcentre M52 for example) come with a
memory chip which cannot address more than 3Gb of physical RAM even if
you plug four 1Gb DIMMs into its four slots. The only reason it has four
slots is for those people with DIMMs smaller than 1Gb.

Although what you say is true, my message quoted above was in response
to someone who is seeing only 2.75GB of the 4GB he installed. I am not
aware of any motherboards or memory chips that have the very odd limit
of 2.75GB.

 

[Swifty]

Although what you say is true, my message quoted above was in response
to someone who is seeing only 2.75GB of the 4GB he installed. I am not
aware of any motherboards or memory chips that have the very odd limit
of 2.75GB.

My thinking was that something might be using 1.25Gb out of 4Gb, but it
was more likely that it is hardware limiting access to 3Gb, and
something (video card?) using the other 0.25Gb.

 

[John John (MVP)]

My thinking was that something might be using 1.25Gb out of 4Gb, but it
was more likely that it is hardware limiting access to 3Gb, and
something (video card?) using the other 0.25Gb.

On a dual Xeon board? Highly unlikely, I wouldn't be surprised if the
board can handle 8GB of RAM.

John

 

[Woody]

I believe that all dual processor boards are 64 bit hardware which would be
able to use all the memory with a 64 bit operating system. The limiting
factor is as specified well above that the 32bit OS can only address 4 gb
and the hardware address spaces need part of that space. The OP mentioned he
has two dual display video cards so that will take a large chunk if address
space.

 

[Cari \(MS-MVP\)]

Not all dual core processors support 64 bit software. Most, but certainly
not all.

 

[Z.K.]

I believe that all dual processor boards are 64 bit hardware which would be
able to use all the memory with a 64 bit operating system. The limiting
factor is as specified well above that the 32bit OS can only address 4 gb
and the hardware address spaces need part of that space. The OP mentioned he
has two dual display video cards so that will take a large chunk if address
space.

If you are using the 64-bit version of Windows XP then you should not
have a problem unless you have bad memory or a bad mother board. I
suspect that you are using the 32-bit version of Windows XP which will
act like you are describing as it can not see the entire 4GB of memory.
I have the same problem, but I am not willing to buy a new Operating
System just yet.

Z.K.