always only by RAM that is listed in the manual. Anything else and you're gambling.
Either way it's a gamble.
Case in point
Corsair is one of the most widely used desktop RAM. It appears in the QVL of virtually every desktop board manufacture, yet suffers compatibility problems even though it is "tested compatible".
Why is this?
Because Corsair use a variety of memory chips within the same model/part number. They differentiate this by adding a version number to the module. The version number is NOT part of the modules part number. I chose Corsair because they appear on the QVL of every desktop motherboard manufacturer
Here's a small selection -and by no means complete:
CM2XP1024-6400
........................XMS640X v1.X...MICRON.......64Mx8...Rev.A
CM2X1024-6400
........................XMS640X v1.X...MICRON.......64Mx8...Rev.A
........................XMS640X v2.X...ELPIDA........64Mx8...Rev.E
........................XMS640X v4.X...QIMONDA....64Mx8...Rev.B
........................XMS640X v5.X...PROMOS.....64MX8...90nm
........................XMS640X v6.X...NANYA.........64Mx8...Rev.B
........................XMS640X v7.X...PSC.............64MX8...90nm
CM2X1024-6400D
........................XMS640X v2.X...PROMOS........64MX8...90nm
........................XMS640X v3.X...ELPIDA..........64MX8...Rev.H
........................XMS640X v4.X...QIMONDA.......64MX8...Rev.C
........................XMS640X v5.X...MICRON.........64Mx8...Rev.D
CM2X1024-6400PRO
........................XMS640X v1.X...MICRON.......64Mx8...Rev.A
........................XMS640X v2.X...ELPIDA........64Mx8...Rev.E
........................XMS640X v3.X...QIMONDA.....64Mx8...Rev.B
........................XMS640X v5.X...NANYA.........64Mx8...Rev.B
CM2X2048-6400C5
........................XMS640X v2.X...QIMONDA......128Mx8
........................XMS640X v3.X...PSC.............128Mx8
........................XMS640X v4.X...MICRON........128Mx8
........................XMS640X v5.X...PSC.............128Mx8
Twin2x4096-6400C5
........................XMS640X v1.X...MICRON........128Mx8
........................XMS640X v2.X...QIMONDA......128Mx8
........................XMS640X v3.X...ELPIDA.........128Mx8
........................XMS640X v4.X...MICRON........128Mx8
........................XMS640X v5.X...PSC.............128Mx8
Twin2x2048/4096-6400C5DHX
........................XMS640X v1.X...MICRON........128Mx8
........................XMS640X v2.X...QIMONDA......128Mx8
........................XMS640X v3.X...ELPIDA.........128Mx8
........................XMS640X v4.X...PSC.............128Mx8
Incidentally, this information cannot be found on Corsair's website- nor is it distributed by Corsair. The full list is being compiled by regular joe's like me and many others in a number of forums to get people with RAM incompatibility problems (including ourselves) a solution.
As a reference here is Gigabyte's P45 DDR2 Memory QVL
http://www.gigabyte.com.tw/FileList/MemorySupport/motherboard_memory_ga-ep45-ds4p.pdf
Notice that the memory IC p/n is missing in Corsair's module listings in many cases.
I consider myself to well schooled in dealing with memory modules and this defeats people who have significantly greater knowledge than I have- including the people to qualify RAM.
Corsair are kind enough to label their memory IC vendor.
Crucial's memory chips are all Micron but like G.Skill, Super Talent, A-Data, Mushkin, OCZ, Kingston, Geil, Aeneon, PQI, Kingmax, Patriot and Transcend, amongst others decline to differentiate their modules based on the chip vendor, IC part number, or in some cases rank and single side/double side configuration.
At the top of Gigabytes QVL list it states in large red type
"Memory modules listed below are for reference only. Due to massive memory models on the market, we can only verify some of them"
Asustek's motherboard memory QVL does not even list the manufacturer of the memory IC's , let alone a part number.
Following Brodie's Memory QVL for the P5Q-SE2 , there are four options available to him for a 4Gb matched set. They are:
DDR2-800
Kingston KVR800D2N6/4G (Elpida E2108ABSE-8G-E, tested but Asus have a ? instead of the latency value. Included in the above list I gave)
G.Skill F2-6400CL5D-4GBPQ (Unknown memory IC, CL5. Included in the above list I gave)
Samsung M378T5263AZ3-CF7 (Samsung K4T2G084QA-HCF7, CL6, Obsolete part number, not available from newegg, tiger direct etc.)
Buy from
http://www.excaliberpc.com/593188/samsung-memory-4g-ddr2-800.html ($142 + shipping, + tax, warranty not listed)
http://www.pc2buy.com/34801/samsung-memory-4g-ddr2-800.html ($145 + shipping, +tax, warranty not listed)
http://www.pinnaclemicro.com/computer/parts.php?g=M378T5263AZ3-CF7&elink=sasfile ($190 + shipping and tax,
90 day warranty)
DDR2-667
Samsung M378T5263AZ3-CE6 (Samsung K4T2G084QA-HCE6, CL5, Obsolete part number)
http://www.upgradebay.com/c1_itemdetail.asp?rid=9&itemid=168783363 ($495 + shipping and tax, warranty not listed)- No other listings for this RAM
The 4Gb Apacer 78.A1GA0.9K4 is also listed in the QVL but seems to be sold exclusively in Southern and Eastern Europe.