- Nov 2, 2006
DDR3 Memory Standards: Blurry Lines
Rated speed, JEDEC, XMP, EPP, overclocking, overvolting... and what it all means
Much confusion has dawned upon many new users. Purchasing memory is not as easy as it used to be. Manufacturers have forced belief that their modules run at certain DDR3 standards. However, what they don't tell you is that these standards [1866, 2133] do not exist. You're required to overclock, modify timings, and overvoltage the memory modules that have these manufacturer rated speeds. So when you plug your memory into your computer and boot it up for the first time, do not expect 1600+ speeds the first time around. You'll at least have to enable XMP/EPP and/or manually configure (timing and voltage) settings in the BIOS.
Now this is where things start to get complicated and full of numbers:
JEDEC is an industry memory standard specification. Manufacturers comply with the JEDEC standard by programming the JEDEC profiles into the SPD chips on the memory. The highest SPD profiles you will find on the market right now are DDR-1333 (some are DDR-1600, but DDR-1333 is the main). This is because the latest Intel CPU platform [Sandy Bridge - P67] doesn't support higher than DDR-1333. This will change in the future, as Ivy Bridge supports DDR-1600 I believe.
EPP (Enhanced Performance Profile):
EPP is NVIDIA's higher-level SPD programming extention. NVIDIA's nForce chipsets can read this SPD extention to provide the much desired "one click overclock." Change a setting and wala, auto-overclocked memory.
XMP (eXtreme Memory Profile):
XMP is Intel's version of EPP that runs on Intel chipsets.
NOTE: EPP and XMP have 2 requirements: your memory MUST have an EPP/XMP profile, and your chipset MUST support XMP/EPP. There are no exceptions to this rule.
The point of all this confusion, and why the manufacturers do it
The most obvious question is why do the manufacturers do all this? Because they want to make more money. The bigger numbers on the sticker means bigger sales.
You would wonder why JEDEC have allowed Intel and NVIDIA to decimate their standard with their "extensions", but nonetheless this is what we're stuck to dealing with.
You bought a P67 board, 2600k and some DDR-2133 memory. You build the computer to find that the memory isn't running at its manufacturer's rated speed (2133), so you take the first step: enabling XMP (this is an Intel chipset, remember) in the BIOS. However, your memory lacks the XMP profiles in its SPD chip so you can't change the setting. You would then consult the manufacturer's website for the settings to be used.
You visit the manufacturer's website, and consult their specified timings for your memory. I've chosen Corsair's Dominator GT 2133C9 in this case (>link here<). If you go to the tech specs section, you shall notice that the SPD speed is 9-9-9-24, DDR-1333, 1.5V which is a JEDEC standard. Corsair's "tested" speed is 9-10-9-27, DDR-2133, 1.65V* which is not a JEDEC standard, but is programmed with DDR-2133 as an XMP profile.
What this tells us is that these are DDR-1333 modules overclocked to DDR-2133 and programmed with an XMP profile to support that without manual adjustment. The actual speed of the module is DDR-1333, but the manufacturer's rated speed is DDR-2133. Like I said previously, manufacturer's rated speeds require at least entering the BIOS and either; enabling XMP, or manually configuring timings, voltage and speed.
If you bought the Corsair modules and tried to run them on an AMD Phenom II system, you would have to input the timings, voltage and speed manually because AMD chipsets do not support XMP. This is a common misunderstanding among many AMD-related visitors of the forum.
Summarising post and final thoughts
- The JEDEC standard of DDR-1333 is currently the highest support on Intel's Sandy Bridge platform. Therefore, whether your memory has regular SPD profiles for DDR-1600+ or not, it will NEVER be set at those speeds.
- Understanding the difference between JEDEC standards and manufacturer's rated speeds. The best hint would be look at the voltage. *JEDEC standards will always be 1.5V or lower; never 1.65V or higher.
- For your memory to work at its manufacturer's rated speed out the box you must; 1) have an XMP/EPP compatible chipset, and 2) have XMP/EPP profile(s) on the memory.
- AMD users will be unable to take advantage of XMP's convenience since their chipsets do not support it. They will have to set their settings manually.
I hope that this has explained a lot of things to some people, and increased their understanding.
Thanks for reading.
Another question to ask yourself: do you really need more than DDR-1333 to begin with? Find some answers and draw your own conclusion - >> P67 & RAM Performance -or- Why DDR3-1333 RAM is enough -> Save the money! <<