| How Core i7 works on the inside Does high Vdimm kill Core i7? Some say yes, some say no... for those of you who remember amd going IMC some years back, you might remember that the 90nm ... |
Does high Vdimm kill Core i7?
Some say yes, some say no...
for those of you who remember amd going IMC some years back, you might remember that the 90nm shrink brought some problems with it... high vdimm could kill or degrade the integrated memory controller. well how did we work around that back then? vcore had to be increased as well to keep the vcore vdimm ratio more or less the same and things were fine. Later when amd moved to K10, the same thing happened again with some imcs dieing at 1.9v ddr2 vdimm if vcore and other related voltages were kept low.well for amds imc implementation the memory controller was actually powered by vcore, so thats most likely why the vcore vdimm ratio had to be maintained. for nehalem or core i7 the memory controller is powered by vtt...
Intel recommends a max vdimm of 1.65v, which is curiously 1.5x vtt...
Several people reported that running higher than default vtt plus higher than 1.65v vdimm works just fine. how come?
From what i know about manufacturing processes, you have to pick the target voltage you want to work with at some point, and then decide what transistor design to use. some transistors can take high voltages but switch slow and are rather beefy, others are small and can switch much faster but will degrade with higher voltages. which is exactly what people reported with vdimm damaged core i7 cpus. one way to work around this and stress the transistors less is by not grounding them to ground but to some other voltage.
I dont know why or how, but vdimm is definately related to vtt, and the fact that intel recommends a max vdimm of 1.5x vtt is not a coincidence if you ask me... its not clear whether this 1.5x ratio exists and if it has to be maintained, or if vdimm has to be within a certain voltage range to vtt, but in either case the resulting highest vdimm/vtt ratios are about the same... once we have relatively cheap 920 cpus available and people can risk burning a cpus im sure it will only be a matter of weeks until we know more about vdimm/vtt on core i7
