Bob said:
Ok, the motherboard is an Asus P7P55D Evo, and the ram is 4 x 2gb of ddr3
There are some more weird experiences here.
http://vip.asus.com/forum/view.aspx..._id=1&model=P7P55D+EVO&page=1&SLanguage=en-us
I'd want to be doubly sure, the system is really reporting "8GB installed".
If it wasn't, there could be a bad stick. I'd probably test the sticks
with memtest86+. Even the response of memtest86+ would be interesting,
in terms of what it thinks is really "installed". Using memtest, helps
eliminate Windows 7 as solely responsible. If both environments see the
same problem, it's a BIOS issue or it's bad memory.
http://www.memtest.org/ (download is half way down the page)
Also, go back into the BIOS, and try with Memory Remapping enabled
and with it disabled. Perhaps one of those options, will cause a
figure greater than 3.5GB to be reported.
The purpose of remapping, is to try to make all 8GB report as
available. It pushes memory, on some quantum boundary, above the
4GB mark. Some server boards, may choose to do a 2GB/6GB split,
which makes no difference as long as remapping is working. In
some cases, the quanta is 256MB, so remapping is on a finer
granularity (not that it matters). The only time it would matter,
if the total address space was limited in some way. Some older
systems, only had 8GB of addresses to work with in 64 bit world,
and would report "7.5GB available", due to bumping into that limit.
On more modern systems, that's no longer a problem.
+-------+ \
| 5GB | \_______
| high | / \
4GB+-------+ / \
| Bus | \
| Addr /| \___ Seamless 8GB in virtual address space
| Video | /
| RAM | /
+-------+ \ /
| 3GB | \_______/
| low | /
+-------+ /
The system busses and video RAM, stay below 4GB, in case some
DMA needs to be done. Some drivers in the past, have been flaky
if add-in cards have their buffers above 4GB. And some PCI cards,
can't do double address cycles, so they're limited to 32 bit
addresses. The end result, is this restriction for safety,
of keeping system busses below 4GB physical.
With 8GB installed, I don't know what a "disabled remap" means.
It could mean, that any memory which conflicts with bus addresses,
is simply ignored. With remap disabled, perhaps you get 3.5GB
from low memory, plus 4GB from high memory. Or, if the BIOS
loads the registers like Top_Of_Memory wrong, only 3.5GB would
be visible. In any case, I recommend fiddling with that setting,
then checking what memtest86+ sees, and check what Windows 7 sees.
Maybe with all the testing, it'll turn out to be a bad stick
of RAM.
Or perhaps you're using XMP RAM (that's a spec for memory, which
allows automatic setup, outside of the JEDEC feature set). I understand
that things like XMP, if you have four sticks installed, can disable
two sticks. (The enhanced speed of the RAM, is only guaranteed with
two sticks, one per channel, and if you enable XMP, it disables
the two extra sticks, on the pretense it allows more speed. Disabling
XMP, means you have to set it up the way you want, yourself.) But that
still doesn't explain why some tools are claiming 8GB is present.
If that was working right, the system should report
4GB present (as the other two sticks are ignored).
Tools like CPUZ can report seeing all the sticks, as CPUZ
reads the SPD bus and reads the SPD EEPROM on each DIMM. But that
isn't quite the same thing, as the BIOS determination of available
RAM. The BIOS reads all the sticks, and programs the memory controller,
including the top of memory register, plus the additional
registers for handling the second chunk of RAM above 4GB mark.
Windows is pretty well stuck with whatever the BIOS does.
The BIOS is also tasked with coming up with a working config,
as Windows is not generally allowed to change it. (The only
option Windows has, it to forbid the system to use some of the RAM.)
You can see some options here, for making Windows ignore some
of the RAM given to it. On WinXP, it would be a simple matter,
to look in boot.ini and see if some option like that was set (MAXMEM).
It might be a slight bit harder to do on Windows 7.
http://msdn.microsoft.com/en-us/library/ff556246.aspx
Good luck,
Paul