I am having a problem with memory timing on my Gigabyte GA-P35-DSL3 using OCZ DDR2-800 1gig x2.
My complete hardware configuration is:
 
 
Intel Core 2 Duo E6750 @ 2.66 MHz
Gigabyte GA-P35-DSL3
OCZ Tech DDR2-800 1gig x2
WD Caviar SE SATA 400gb
e-GeForce 7600GT
Samsung 22" SyncMaster LCD
 
 
While trying to install the OS (Fedora Core 7 x86_64) I was experiencing crashes, freezes and video weirdness, like random cyrillic chars on the screen.
Memtest86+ showed no errors in 8 passes.  Mobo POSTs without problems.  Hard disk tests passed, read, write, surface.
Samsung monitor worked flawlessly hooked to my older machine, using the new display card and the old.
 
 
I posted my problem on Fedora Forum and found a partial answer, which was to "clock down" the memory to 667 MHz from 800.
Once I did, Fedora installed, and has run well and stable since, even with the nVidia driver kernel mod.
This issue is not related to what some are experiencing with nVidia drivers on Fedora Core.  The display drivers work great.
I had hoped to be able to clock back up after the install.  No go.  Same problem when "pushed" to 800MHz.
 
 
Now I would like to see if I can bring the memory back up to 800MHz, which I understand is a standard for this mobo and memory, or at least that is what the memory sticks are rated for.
When I set the memory to 800MHz, or what the BIOS considers "optimum", the freezing and random error borkage comes back.
I don't want to damage my fresh install with more tests.
I want to get good information on what to try, and limit the possibility of write errors to the drive.
 
 
Has anyone else encountered this?
I can't be the only Fedora Core x86_64 user out there, logically.
 
 
I have built several machines, but not a Core 2, so that part is new to me.
The computer is quite stable currently, and has been rock solid for over two weeks.
I'm not looking to overclock, just get the memory chips going at 800MHz clock speed, if possible.
Is this something that only affects Fedora Core Linux x86_64 users, or is it OS independent?
Is there a combination of setting in the M.I.T. BIOS area that I need to set together to achieve the correct result?
I am loathe to mess around with various settings, only to cook my system, or bork my BIOS.
I searched the forum and found nothing directly related to this issue at the time.

I know nothing of linux, but I can't imagine why an os should care about hardware memory speeds.  As a guess, You could try upping the memory voltage a bit if it is lower than the specs for the memory.
 
On the other hand, do you need to?   The C2D processors are not sensitive to memory speeds.   For a real applications(vs. synthetic benchmarks)  the difference in performance between the slowest and fastest  memory  is < 2%.  If you are overclocking, then that is a different matter.

 
Geofelt,
Thanks for the prompt reply.
Fedora Core kernel code has the ability to adjust CPU speed depending on load.  
 It's a daemon called cpufreq.  According to the doc that I read, it doesn't apply to the Core 2 Duo.
It's actually comforting to know that the Core 2 Duo is not sensitive to memory speed.
 
I don't know what the voltage specs are for these memory sticks.  Does anyone know?  I'm curious.
Less than a 2% gain is not worth trashing a clean install, IMO.  
I don't plan on overclocking.  I'm not opposed to it, I just don't know enough about it to venture into that territory as yet.
I'm looking for a stable, reliable machine that will last awhile, so maybe I'll wait, or not do anything until I upgrade the memory to the faster 1333MHz bus speed.
The gain with the current memory is not great, and the risk is high.
Besides, this is already a screaming fast machine, at least to my eyes.
I can play about in Second Life, and do ten other tasks without any change in performance.  Truly amazing.
I checked the BIOS revision, and everything is up to date, thankfully, so I will leave well enough alone,
and resist my urge to tweak, however strong.  Heh.

OCZ makes lots of memory.  If you can run cpu-z, the memory tab should show you just which model you have.   It should also be printed on the sticks themselves.

You should be aware that many types of enthusiast memory are rated at optimal clock and timings at 2.2v while some motherboards (mine, a GA-M61P-S3, for example) are only rated at 1.8v stock. I can't get mine to a stable overclock without changing the voltage in the BIOS.

 
Didn't find a version of CPU-Z for Linux, although I recall a port somewhere....  Darn you Google!  Don't fail me now!  Oh well.
No matter.  I found the info:
http://microcenter.com/single_prod [...] id=0242908
 
"The new OCZ PC2-6400 Revision 2 Platinum Edition utilizes the latest OCZ heatspreader design. XTC (Xtreme Thermal Convection) Heatspreaders allow increased ventilation and heat dissipation due to an innovative honeycomb design providing more direct access to the actual memory ICs. At DDR2-800, these modules turn out heart-pounding 4-4-4 timings with flawless performance and stability."
 
2.1 Volts  Unbuffered  Non-ECC
 
So, the question now is, is there a way to make these memory chips clock at 800MHz, and if so, is it worth it?
Thanks for all the replies, I appreciate it very much.
 
P.S.- I'll bet you all didn't know that "heatspreader" is all one word.  Heh.

It's probably worth a try to set the memory to 2.1 volts, and see how you do.  

 
 
Very good.  Are there other timings that need to be set along with this, or just the memory chips?
I'll try it, until I smell smoke.  Heh.