[Leaplist] Only seeing 3G memory

[Bryan J. Smith]

From: Gray Frost <grayf327 at gmail.com>
> I hear what you are saying about motherboards and chipsets
> not able to read more than 4 gig but this one is advertised
> and reviewed as having that capability.

Sometimes they market 64-bit as "breaking 4GB."  Other times
they will, as long as you have 6GiB or 8GiB, but they won't
page the memory mapped I/O under 32-bit/4GiB above it.  And
yet other times they just don't do it right at all.
 
> This is my uname -a
> [root at localhost ~]# uname -a
> Linux localhost.localdomain 2.6.25-14.fc9.x86_64 #1 SMP Thu
> May 1 06:06:21
> EDT 2008 x86_64 x86_64 x86_64 GNU/Linux

I was looking for:  x86_64 x86_64 x86_64
To confirm you are actually "Long Mode" (52-bit PAE addressing)

It should map in the memory above 32-bit/4GiB that is used
for memory mapped I/O under 32-bit/4GiB.

Probably my next move is to get the start of your dmesg to
see if I can see how it's mapping memory.  I know there are
probably some other /sys details I'm not thinking of, more
than just /proc/memory.  Things that show the mapping/paging.

But if the BIOS is saying it, hmmm.  That's never good.

- Here's another thought ... the actual DIMMs?

What are your DIMMs BTW?  One might not be used.  That's
the other thing I have to consider.  Especially if you now
have four (4) DIMMs and it's Socket-754.

JEDEC specifications allow only up to three (3) DIMMs per
DDR-200/PC-1600 channel, two (2) DIMMs per DDR-266/PC-2100
or DDR-333/PC-2700 channel, and only one (1) DIMM per
DDR-400/PC-3200 channel.

Mainboards should slow the signaling to allow more per channel.
So on a Socket-754 (single channel DDR), it should slow to allow
up to three (3) DIMMs at DDR-200/PC-1600.  If you have four (4)
DIMMs in a Socket-754 mainboard, then that's definitely well
beyond what any DDR signaling can handle on a single channel.

If it's Socket-939 (dual channel DDR), then it might be a sizing
issue.  If you stick in a DIMM technology that is double the
RAM technology supported, it will show up as only half.  So
if you just added two (2) DIMMs, 1GiB/each, and you're only
getting 3GiB, then there's the possibility that it's only
addressing 512MiB on each DIMM (for +1GiB).  It's been a long
time since I've seen anything like that, but it may be possible
that you have an early Socket-939 chipset that did such with
certain RAM IC combinations that are newer than it is designed
for.

If it's Socket-AM2 (dual channel DDR2), then that's really weird.
A pair of 1GiB DDR2 DIMMs should have no issues on any Socket-AM2
platform.  The only thing could be if someone sold you a
2GiB kit (2x1GiB) that was actually only a 1GiB kit (2x512MiB).
If you have Socket-AM2, I have extra, 1GiB DDR2-667/PC2-5300
DIMMs you can try.  They are HP DIMMs with Micron ICs.


-- 
Bryan J Smith        Professional, Technical Annoyance
b.j.smith at ieee.org  http://www.linkedin.com/in/bjsmith
------------------------------------------------------
I'm a PC, but Linux -- Windows: Life Without Firewalls


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