Ppls like to think any single specific prob has just one cause for the most part, but with this prob it just isn't true.
There are perhaps a dozen causes of this prob, and none seem the most common.
I see some ppls saying they read all the threads about this, they tried all that, and yet they say they are using "XMP memory profile." BUUZZZZ! WRONG!
I trust you are using the correct slots? NOT the black ones.
ALWAYS enter your mem latencies (first four and maybe command rate) manually, and your mem V, and set the mem multiplier ("Memory Frequency") manually, don't forget to drop it as needed when OCing. MCH strap "DIMM ratio" seems to work for some ppls, esp those with BIOS 76 or later, "auto" seems to work for others.
Although some ppls do fix their mem prob in BIOS, don't assume there is a fix without physically taking things apart again. Don't be reluctant to reseat stuff - including your CPU cooler. Don't tell us you did when you didn't, just bc you are convinced it is not a hardware seating issue. I've personally noticed that often the mem is wicked hard to seat completely, I've had to push so hard I have worried about breaking the mobo. One time (after no probs) I noticed in my recent pics a mem clip was not fully engaged (I fixed it). A couple of ppl have reported they fixed theirs by 'sliding the ram back and forth' (the tiny bit of play in the slot) as they pressed it in.
BIOS revisions, other than the revisions listed here, seem to have nothing to do with this problem. If you think you have fixed it with a BIOS revision I propose that the other revision had a different setting somewhere. Exception: BIOS revisions since 76 have had a tRL setting in which a "+2" setting may work for some, only when OCd. And BIOSes 41 thru 69 would not do 2:8 properly, and 4x and 5x series BIOSes were just plain duds otherwise as well.
If you have more than 16GB, don't expect to OC over 4.0GHz (Bclock 190 in i7-920) without mem dropping out. This is due to a weak mem controller in the core i7 series, and swapping CPUs (different or same) may affect this - different chips have slightly stronger mem controllers, it seems to be luck-of-the-draw. As a matter of fact, RMA of CPU has remedied the 'not all memory useable' issue for a couple of ppl on this forum - and they said they had no prob's W/Intel on the RMA.
Never reload a previously saved BIOS profile after flashing your BIOS. Safe practice is to immediately save all 8 BIOS profiles after flashing BIOS and resetting CMOS (with PSU on, computer mobo off) - to clear them out (the different BIOS revisions use different CMOS addresses to save this data). If you have done this, you need to reset CMOS and start from scratch again.
Did you run Memtest86+, v4.x (4.2 is current ver,
http://www.memtest.org/ ), with default BIOS settings except your RAM numbers plugged in, overnight, before you did anything else like install Windows? No? Did you try it lately? If you have errors, you may need to reinstall Windows after fixing your RAM prob.
If you are having this prob when OCd, try backing off the OC quite a bit. If it restores the mem, then find the threshold where the prob begins (within 2 Bclocks, or one multiplier). This would indicate your mem prob is probably not a physical one (not a seating issue). Then troubleshoot your mem prob at that OC level bc you may never resolve it with your CPU/mem at the previous OC level.
If you have the 'not all memory useable' issue at stock CPU clocks/multipliers, you probably will never be able to resolve it via BIOS settings with CPU OC'd, unless you solve it first at stock clock.
Memory not all being used issue threads:
This is the best thread so far for this subject, is 5 pages long, this thread should be a sticky:
Disappearing Ram Dont miss page 5
This one has a Blue-ribbon post by MoltenLava where he recommends sliding the RAM as you seat it:
Re:i7 920D0 + Classy E759 = not all RAM there - Post #3 Some more of them:
Problem 6.00GB = 1.99GB usable? Windows 7 x64 Ultimate Disappearing Ram... 6GB ( 3.99GB usable) HELP! 3.99GB Usuable with 4.0GHz OC and Stock it shows full 6GB RAM 3.99GB usable E758 All Ram Not Recognized Issue X58 SLI LE..6gb (3.99 usable) Loosing RAM in windows (and/or BIOS) after a cold boot:
X58 E-758 missing RAM and graduate to this one:
Disappearing Ram Using older BIOS:
Re:Best BIOS Version for EVGA X58 SLI E758 - Post #12 linuxrouter 7/9/2010 -
"For my E758 with a 920, I have tried a variety of newer BIOS versions including 44 and 73 but ran into intermittent system crashes. I keep the system loaded 24/7 and running Linux and generally between 24-48 hours I would see a crash. I am back on SZ2S and the system has running stable for the past two weeks or so."
post edited by HalloweenWeed - 2013/02/15 18:37:14