4 Gb of ram detected as 3

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bdzyub

Hello!
I have this wierd problem with a XPS 720. I have it with 4GB of
memory (4x1024 mb). Windows XP 32 bit detects it only as 3GB under my
compluter and the task manager. CPUz shows all 4 slots filled
though.
Can anyone please help and explain this to me.
Thank you in advance.
 
Hello!
I have this wierd problem with a XPS 720. I have it with 4GB of
memory (4x1024 mb). Windows XP 32 bit detects it only as 3GB under my
compluter and the task manager. CPUz shows all 4 slots filled
though.
Can anyone please help and explain this to me.
Thank you in advance.
Click to expand...

There are some examples of what to expect in the back of
this document.

"Intel Chipset 4 GB System Memory Support White Paper February 2005"
http://dlsvr01.asus.com/pub/ASUS/mb/4GB_Rev1.pdf

Paul
 
Hello!
I have this wierd problem with a XPS 720. I have it with 4GB of
memory (4x1024 mb). Windows XP 32 bit detects it only as 3GB under my
compluter and the task manager. CPUz shows all 4 slots filled
though.
Can anyone please help and explain this to me.
Thank you in advance.
Click to expand...

that's normal for a 32 bit system.............mine only shows 3.25.
 
I guess I should just go for the 64 bit version then...
Click to expand...

If i remember correctly... 32-bit systems can only address 4GB.
Problem is PCI cards also use address space, working out to about
250meg worth each i think. So you probably have 4 PCI cards in your
machine (4x250MB = 1GB missing RAM). If you take 1 PCI card out, you
should notice windows reporting your RAM as 3.25GB.

Somebody correct me if i'm wrong here, but there is no way around this
unless you upgrade to a 64-bit OS, which of course comes with its own
limitations :)
 
If i remember correctly... 32-bit systems can only address 4GB.
Problem is PCI cards also use address space, working out to about
250meg worth each i think. So you probably have 4 PCI cards in your
machine (4x250MB = 1GB missing RAM). If you take 1 PCI card out, you
should notice windows reporting your RAM as 3.25GB.

Somebody correct me if i'm wrong here, but there is no way around this
unless you upgrade to a 64-bit OS, which of course comes with its own
limitations :)
Click to expand...

There seems to be some minimum allocation. So if a PCI card needed a
megabyte of address space, the BIOS would allocate 256MB. And if the
PCI cards needed a total of 257MB of address space, the BIOS would
allocate 512MB. PCI Express might cause something similar to happen.
And AGP aperture also takes a chunk, if AGP is present. (The various
Intel documents, like the chipset datasheets, usually have a section
that explains it.)

About the best you can do, is unplug all PCI Express cards, disable
PCI Express peripheral chips, unplug an AGP card if present, and use
a PCI video card. Then the address space might be 3.5GB or a bit
more. But who wants to completely hobble the computer, for a few
extra bytes ?

For some people who had two PCI Express video cards (for SLI usage),
I think they got 2.75GB in Windows. But if they want SLI and decent
sized texture memory, that is the price they pay.

The OP should continue to use the four sticks, because the memory
controller will run in dual channel mode that way. 4x1GB matched,
runs in dual channel. 3x1GB is unbalanced, and runs in virtual
single channel. 2x1GB + 2x512MB runs in dual channel mode, with the
loss of the ability to use certain interleaved memory controller
modes (but the performance loss in that case is minimal, so that
is a viable alternative config). But if you've already paid for
the memory, and the vendor won't take it back, 4x1GB with a little
wasted, isn't so bad.

Paul
 
So if I upgrade to Windows XP 64 bit, since it can address a lot more
than 4GB, then it will see all of the memory while still addressing
the PCI cards?
 
32 bit OS's, such as XP, can only recognize up to 3.2 GB of RAM. The same
limitation applies to consumer oriented motherboard BIOS's: they only
recognize up to 3.2 GB of RAM, even if you install 4 GB.
To recognize more you have to go to a workstation motherboard and a 64 bit
OS.
 
So if I upgrade to Windows XP 64 bit, since it can address a lot more
than 4GB, then it will see all of the memory while still addressing
the PCI cards?
Click to expand...

There are a couple kinds of desktop chipsets.

1) 4GB total memory, with no memory remapping function.

Compare Table 2 to Table 3 on page 18. *It didn't help*
The 915 is an older chipset.

http://dlsvr01.asus.com/pub/ASUS/mb/4GB_Rev1.pdf

2) 8GB total memory capable chipset, with memory remapping
function. Assume we plug in 4GB of memory. From 0 to 3GB,
we see the first 3GB of memory. Then from 3GB to 4GB, we
have address space for PCI, AGP, PCI Express etc. Then,
the last 1GB of memory, is "hoisted" to the area from
4GB to 5GB. This "remapping" or "hoisting" function is
key. Athlon64 has hoisting built into the processor. For
Intel, you have to read the motherboard chipset datasheet.

Knowing what the chipset is, you can look up whether it
"hoists" or not. If the chipset doesn't "hoist", WinXP 64
won't help solve the problem. Comparing Table 2 to Table 3
in the above document, shows what happens when there is
no "hoist".

And to help matters, the BIOS may not use a very meaningful name
for the function. In this BIOS, the "hoist" is:

"Memory Hole For PCI MMIO"
http://www.fileshosts.com/memory/crucial/4GB_DFI_NF4bios/PCI_MMIO_4GB_bios.jpg

OK, so I looked up your computer, and it looks fine. Like the
"Memory" section here says, if you use WinXP 64, it'll take
8GB of memory. Memory above 3GB, is hoisted to the zone above
4GB.

http://www.dell.com/content/products/productdetails.aspx/xpsdt_720?c=us&cs=19&l=en&s=dhs&~ck=mn

Paul
 
Dell claims that the computer should eb able to adress up to 8 GB of
ram with a 64 bit operating system. I am assuming that this means
that it does hoist the extra 1GB of ram?
 
On Thu, 13 Sep 2007 06:24:32 -0000 (e-mail address removed) wrote:

| I thought that a 32 bit system should be able to adress all 4GB?

Yes, a 32-bit system can address all 4GB. But if you fill all 4GB with RAM,
there's no place remaining for other stuff the system needs like devices,
ideo and BIOS. That's why the old 16-bit computers (20 bits of address
after segmenting) could only do 640K instead of the full 1024K the 20 bits
should in theory allow. BIOS, video, and other things, were located above
that 640K line (and your machine still has stuff there when it first starts
up in legacy "real mode").

32-bit systems do have a "PAE mode" that extends addressing to 36-bits. But
Windows drivers will need to be passed a 64-bit data type to get addresses
higher than the 4GB line, so you could run into all the same compatibility
issues with some drivers as you would with a genuine 64-bit machine. Linux,
if you are using that, handles PAE a little better, but it slows down the
drivers. I also heard that SP2 of XP basically crippled PAE handling.

If you can't live with 3GB or a little more than that (I've read that some
people managed to configure their machines for as much as 3.75GB usable),
then you'll need to go with a 64-bit machine. But if you do that, and run
64-bit apps, add at least another 2GB of RAM (now 6GB at least) to adjust
for the expanded _usage_ of memory that 64-bit code causes (all addresses
and memory size values in the code take twice as much memory).
 
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