[Leaplist] Only seeing 3G memory

[Bryan J Smith]

Gray Frost wrote:  
> In the Extended Memory section of the bios
> setup utility it shows 2881536k which is what I
> am seeing with the software.

How much is being used by the integrated graphics?
That's what I'm curious to know. ;)

> I did some testing with each and every memory
> chip by starting off with each one all by its
> lonesome in the first of the four slots (blue slots).
> They all showed 1gig as seen by the bios.  So no
> reason to suspect the memory.
 
You just tested single channel, single DIMM.

So on their own, no, nothing to suspect.
In dual channel, probably not.
But switching between dual-channel banks, maybe.

> Then I added each one individually to slot number
> 2 (blue slots so far)  and combine for every one
> was 2G as seen by the bios.  Good this make since

And now you've tested dual channel, single DIMM
(in each).

You should also try (but not run as permanently) single
channel, dual DIMM by putting them in 1+3.

> This is where it gets interesting and I am not very experienced?
> I added each of the remaining memory sticks to the
> third slot (first slot of black) and the bios still only
> showed 2 gig.  This did not make since to me so I
> removed and tried each in the fourth slot and still
> the bios only showed 2G.  ARRR??
 
Coreect.

When you use 1+2, the system detects dual channel.
So you have to add 3+4 for it to work.  Adding just
3 or 4 will not, because 1+2 enables dual channel.

I'd be curious to know what happens if you put 1+3 and
then add 4. It would probably see 3+4 and dual-channel,
so it would still be only 2GiB.

> When I put both in the third and fourth slot (both
> blacks) then I get the 2882560k.   Ok so the
> individual slots third or fourth slots don't register
> any additional change from 2gig but having both of
> them adds the  0.8Gig. 
 
Actually, you get 4GiB. The problem is the mapping.
- How much is used by mapped I/O?
- Why isn't the real memory that overlays it mapped
   above 4GiB (so it can be used by the x86-64 kenrel)?
- And just how much memory is reserved ("lost to")
   Integrated graphics?

I guess I didn't explain this better ...

On any PC, you can _never_ access all memory below 4GiB,
so is addressed for memory mapped I/O and other things.
So the mainboard should "bounce" that memory to above
4GiB so x86-64 (and i686 PAE) kernels can use it.
If a mainboard does not do this proper, the kernel may
not get to use it. I say "may" because Linux/x86-64
(or even i686 PAE) can, many times, recover that
memory anyway.

In your case, it's not, which means the mainboard/BIOS
really has issues, and is preventing the kernel from doing
even that. Again this is why I also asked how much memory
you have reserved for integrated graphics. I'm curious
if you realy have that jacked up high too. ;)

> hmmm  this is why I was wondering if there was something
> in the bios i need to set to get it to read all four gigs.

Again, the system is "seeing" all 4GiB, but _no_ PC can
_ever_ access all 4GiB under 4GiB, hence why it is less.
It's why Windows Home/Pro can only support 3GiB (no
PAE
support), and why you have to load a x86-64 or i686 PAE
kernel to access al 4GiB.

Some mainboards map correctly, and report correctly.
Others do not, but don't inhibit the OS from doing so.
And many other stiil don't and don't have support for
and/or inhibit the OS from doing so.

> Maybe flashing with a newer version of the bios?

That was my absolute first suggestion because this
issue goes both back 5 years to the original Opteron
servers as well as just the last few years of cheap
Athlon 64 mainboards.

The mainboard has to map some of the last 1GiB or so
above 4GiB, or at least not inhibit the OS from doing so.
Also, check that video reservation! ;)
--  
Bryan J Smith - mailto:b.j.smith at ieee.org  
http://thebs413.blogspot.com  
Sent via BlackBerry from T-Mobile  
    
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