XMP and the Real World

First off, lets see what bobnova says about XMP profiles:

XMP stands for Intel eXtreme Memory Profile, it's a standard that Intel came up with to supplement JEDEC's ram SPD profiles. What, that wasn't a useful description?  Ok, well here comes the long version!

JEDEC is the outfit that defines memory types.  DDR3?  Designed by JEDEC.  DDR2?  Deisgned by JEDEC.  They come up with the basic design and protocal for a type of ram, and set some basic speeds and timings and voltages that can be used.  For DDR3 you can have 800mhz, 1066mhz, or 1333mhz.  That's it, no more.  At the same time you're limited to 1.5 volts.

Now some ram can go pretty fast on 1.5 volts, but not much.  Most requires more to really get flying, but if it isn't 1.5v they manufacturers can't save a profile in the ram for the BIOS to automatically use, it's simply impossible.

This is where XMP (and EPP, the older DDR2 version from nVidia) comes in.  It's published by Intel and allows plenty of voltage as well as speeds that aren't officially JEDEC DDR3. 

This sounds great, but it has a major drawback, namely that what is stored in an XMP profile has to work on every system it could possibly be plugged into.  This is an issue for two reasons, the first is that ram manufacturers simply don't have the time to test every single kit of ram to see how fast it will really go.  The second is that ram manufacturers can't test every cpu the ram will be used on, and every single CPU ever made requires slightly different amounts of voltage to run a given ram speed.

Why is this an issue?  Because it means that the voltages in the XMP profile are generally set so that they'll work on all cpus, in the case of very fast ram (like this kit) this means a lot of voltage, probably more then the CPU needs, and someitmes enough that it will do damage to the CPU over time.  That's a problem!

The only other option is for them to leave cpu voltage out of the XMP profile entirely and let the motherboard BIOS try to figure out what is needed.  Then it's the motherboard that risks frying the CPU and getting it's manufacturer in trouble.  On the plus side to that approach, motherboard manufacturers have a much better idea on voltage then ram manufacturers do, they've already tested a lot of cpus with their motherboards.

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