Installed 4 GB of memory; only able to use 3,406,240 Bytes

[Charles Elliott]

Hello:

I installed 4Gb of memory under WinXP, but Task Manager indicates only
3,406,240 bytes

are available for use. Does anyone know why that is? Is there any way to
get WinXP to use

the full 4GB?


Thanks,

CHE

 

[JS]

In round numbers XP can only address 4GB.
Your video card has XXXMB of ram on the card so
that limits XP to 4GB minus the cards XXXMB of memory.

In addition other hardware also takes away additional amounts of memory
(usually a small when compared to the video card)
and the remaining memory (address space) is available for
Windows XP and your applications.

So most of that 4th GB of ram you installed (in your case about 600MB)
goes unused.

A link to the white paper titled "Gaming Performance Analysis" by Corsair
Memory Inc. provides a good clear explanation of how a video card effects
the amount of available memory in your PC.
See: http://www.corsair.com/_appnotes/AN804_Gaming_Performance_Analysis.pdf

Intel Chipset 4 GB System Memory Support
http://www.dcomputer.com/ProInfo/support/support/mainboard/4GB_Rev1/4GB_Rev1.pdf

Vista Users with SP1 now report how much physical memory installed on your
computer:
See: Windows Vista SP1 includes reporting of Installed System Memory (RAM):
http://support.microsoft.com/kb/946003

JS
http://www.pagestart.com

 

[Ken Blake, MVP]

I installed 4Gb of memory under WinXP, but Task Manager indicates only
3,406,240 bytes are available for use. Does anyone know why that is? Is there any way to
get WinXP to use the full 4GB?

No, there is not.

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.

By the way, why did you install so much? Regardless of the point
above, it's very rare that an XP user needs or can make effective use
of even the 3,406,240 bytes that you get.

 

[Faustino]

Ken, I added a further 2Gb to my existing 2Gb Kingston Value DDR2 800 (PC
6400) RAM because (a) I might get better gaming performance with > 2 Gb; (b)
it was very cheap at the time - prices vary a lot, as does the value of the
$A; (c) even if I can't use it all (XP Pro indicates 3.25 Gb), I have four
identical sticks of 1 Gb RAM, very handy if one fails - hardware moves so
fast that I'd be unlikely to find matching RAM later (would that matter?
Well, I won't need to fi nd out).

 

[Ken Blake, MVP]

Ken, I added a further 2Gb to my existing 2Gb Kingston Value DDR2 800 (PC
6400) RAM because (a) I might get better gaming performance with > 2 Gb;

Even 2GB is much more than most people can get better performance
with. Most people see no improvement by going over 512MB or so, but
whether more than that improves performance depends on what apps you
run. Some apps can make effective use of more RAM.

Which games you play might make a difference, but since I don't play
any computer games, I personally couldn't tell you which ones would
benefit by more RAM.

(b) it was very cheap at the time

Understood, but whether it helps you, I don't know.

- prices vary a lot, as does the value of the
$A; (c) even if I can't use it all (XP Pro indicates 3.25 Gb), I have four
identical sticks of 1 Gb RAM, very handy if one fails - hardware moves so
fast that I'd be unlikely to find matching RAM later (would that matter?

Yes, it matters. Non-matching RAM can cause severe problems.

Well, I won't need to fi nd out).

 

[Swifty]

No, there is not.

It's probably too late to worry about this in 32-bit Windows, but I used
to work with IBM mainframes which used 24-bit addressing, so could only
use 16Mb. However, the virtual storage hardware could address 64Mb, so
you could map four 16Mb address spaces into 64Mb real, with no paging.

I've often wondered if the "inaccessible" memory above the limit could
be used in this way, or as a very fast, 1st level, paging device. Of
course, this is more of a hardware issue than an XP issue.

 

[JS]

Somewhat along the lines of the old LIM 4.0 specs.

JS
http://www.pagestart.com

 

[Jim]

It's probably too late to worry about this in 32-bit Windows, but I used
to work with IBM mainframes which used 24-bit addressing, so could only
use 16Mb. However, the virtual storage hardware could address 64Mb, so you
could map four 16Mb address spaces into 64Mb real, with no paging.

I've often wondered if the "inaccessible" memory above the limit could be
used in this way, or as a very fast, 1st level, paging device. Of course,
this is more of a hardware issue than an XP issue.

It certainly could use the unusused RAM in such a fashion, but not without
lots of added software.
Jim

 

[Unknown]

Only 16 meg with 24 bit addressing????? Please explain.

 

[blank]

2^24 = 16777216 = 16MB

The original IBM PC had 20 bit addressing, which is why it could only
address 2^20 = 1048576 bytes (1MB)
The A20 line (the 21st bit), was used to access "upper memory", where
memory above 1MB could be mapped in (using something like HIMEM.SYS to
control it).

32 bit addressing gets you 2^32 (4GB) of address space. Various hardware
like video cards, network cards, and other peripherals or motherboard
resources occupy some of this memory space, usually leaving you with
around 3.5GB or less of addressable memory. Later service pack updates
to WinXP limit you even further than this, to around 3GB.

64 bit addressing gets you 18446744073709551616 addresses

Only 16 meg with 24 bit addressing????? Please explain.