4G vs 3G of RAM

[sjc]

If I install 4G of RAM I get the following:

The My Computer | Properties | General shows 2G of RAM
and the System Information shows:
Total Physical Memory 4,096 MB
Available Physical Memory 1.7 GB

If I install 3G of RAM I get the following:

The My Computer | Properties | General shows 3G of RAM
and the System Information shows:
Total Physical Memory 3,072 MB
Available Physical Memory 2.7 GB

WIth 1G less RAM the Available Physical Memory increases by 1G.

My hardware is a Core 2 Duo 6600 and the Intel 975 chip set with XP Pro
SP2.

What's going on here? Does XP do better with 3G then 4G. I have tried
boot.ini switches /3GB /PAE which have no effect.

 

[R. McCarty]

How is your BIOS configuration for Dual-Channel operation set ?:
If Dual-Channel operation is enabled and you don't populate both
slots for the channel you'll see misreporting like you describe.

 

[Rock]

XP can only run on 4G or less,if you go over 4G,even by a small %,the
system
must revert to the allowed default amount which also means it will
eliminate
most for it to use some.If you installed 3.99.999 You get that much
alocated,but
even 4.00001 is over.

Lol, Andrew E., get lost you troll. He said he installed 4GB which is
4x1024 which is 4096MB which is what is being reported, which is not 1 byte
over 4GB.

 

[sjc]

The BIOS auto configs so when 4G installed dual channel when 3G
installed not dual channel. But don't understand how this could make
difference since System Info reports the right amount of RAM.

 

[Kerry Brown]

It's probably something in the way your motherboard maps the ram. The top of
the 4 GB address space is taken up by motherboard resources. Some
motherboards try to play tricks with this and remap ram that is trying to
use this space to up above 4 GB. The motherboard resources have to stay
below 4 GB for 32 bit driver compatibility. There may be BIOS settings you
can change that will affect this. Switching to a 64 bit OS may also fix it.
In any case with 4 GB installed in 32 bit Windows you will be lucky to see
more than 3.25 GB reported by Windows.

 

[Tim Slattery]

XP can only run on 4G or less,if you go over 4G,even by a small %,the system
must revert to the allowed default amount which also means it will eliminate
most for it to use some.If you installed 3.99.999 You get that much
alocated,but even 4.00001 is over.

Huh??? XP has a 4GB address space, nearly all machine that 32-bit XP
runs on - especially home machines - won't allow you to put in more
than 4GB. Some of that address space must be used to access video
memory and other memory and registers presented by PCI and PCI Express
cards. (see http://members.cox.net/slatteryt/RAM.html), so if have 4GB
of RAM in your machine, you won't actually be able to use it all. The
/3GB switch has nothing whatsoever to do with this, the referenced web
page discusses this also.

But none of that explains what's happening to OP.