Windows XP Physical Memory Limitations

[MPH-101]

I have an HP system running Windows XP Media Center Edition 2002 (SP2) that I
recently upgraded the RAM on since many of my applications and simple
Internet activities where thrashing the harddrive to death (I only had 512MB
of RAM before the upgrade). I now have 4GB of DDR2 RAM and the HP system
software recognizes all 4GBs of physical memory, so the installation is OK.
However, Windows only recognizes 3.11 GB. My system has a 3.06 GHz Pentium 4
CPU, for what that's worth. Many years ago when I used to really get into
operating system design, and the like, I used to have to create workarounds
with the memory limitations of MS-DOS and early versions of Windows (e.g.,
the old 512k limit in DOS and, hence, Windows 3.1). I have now evolved into
mostly a user these days and do not understand the newer versions of Windows
like I did the older versions. Am I up against a memory limitation with XP?
If so, is there a workaround that will allow me to use all 4GBs of RAM? Or
will I have to upgrade to Vista (yuk!)? Thanks for whatever assistance
anyone can provide.............

 

[Unknown]

4 Gigs cannot be addressed because some of the address bits are used for
other purposes. It is the hardware
architecture that limits it. Your computer is working correctly.

 

[Ken Blake, MVP]

4 Gigs cannot be addressed because some of the address bits are used for
other purposes. It is the hardware
architecture that limits it. Your computer is working correctly.

No, there is no workaround, and it would be exactly the same in Vista.

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.

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 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.

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.

 

[Bob Knowlden]

The limitation is in desktop 32 bit Windows operating systems. (It also
applies to 32 bit versions of Vista.) Google would show you more hits on
that than anyone would care to read.

A 64 bit OS (XP 64 or Vista 64) would fix that. I'm not a software
professional, so I don't know whether any of your applications would benefit
from a 64 bit OS, but I imagine that you have no 64 bit applications. (32
bit applications run fine for me under Vista 64.)

If you needed more than 4 GB of RAM, you'd have no choice: the 32 bit OSes
don't support more than 4.

Return address scrambled. Replace nkbob with bobkn.

 

[PD43]

4 Gigs cannot be addressed because some of the address bits are used for
other purposes. It is the hardware
architecture that limits it. Your computer is working correctly.

However, his paragraphing isn't.

 

[db ´¯`·.. >]

perhaps the /pae
switch might provide
be of benefit:

http://msdn2.microsoft.com/en-us/library/aa366718.aspx

 

[HeyBub]

I have an HP system running Windows XP Media Center Edition 2002
(SP2) that I recently upgraded the RAM on since many of my
applications and simple Internet activities where thrashing the
harddrive to death (I only had 512MB of RAM before the upgrade). I
now have 4GB of DDR2 RAM and the HP system software recognizes all
4GBs of physical memory, so the installation is OK. However, Windows
only recognizes 3.11 GB. ... Am I up against a memory limitation with
XP? If so, is
there a workaround that will allow me to use all 4GBs of RAM? Or
will I have to upgrade to Vista (yuk!)? Thanks for whatever
assistance anyone can provide.............

You are using the 32-bit version of XP.

2^32 = 4,294,967,296 is the most number of bytes XP can access. Subtract
those mandated for use by various hardware pieces and you're left with the
3.11GB shown (after making allowances for 1 GB = 1024 MB, 1 MB = 1024 KB and
other nerdish shorthand).

Upgrading to Vista-32 won't help. You can upgrade to XP-64 or Vista-64.

But all this begs the question: Did your hard drive quit thrashing?

If not, the cause of the thrash is something else and you just wasted your
money.

If your hard-drive DID quit thrashing, then your question here is more of a
curiosity item.

 

[Colin Barnhorst]

What are you doing that you feel you need additional ram for? If you have a
program that requires more ram than is supported by XP x86 then migrate to a
64bit computer and operating system. The 3GB that you are reporting is
simply the portion of the 4GB total that is available for user programs.
The system is allocated the remainder as described by others already. That
is the trade off for the high end video cards and other devices in use
today. Essentially, there are two of you using the computer; you and the
computer.