Tuesday, September 2, 2014

X99 VRM Analysis

X99 has arrived and what most reviewers seem to have missed is that Intel's FIVR is on every Haswell-e chip. The FIVR stands for Fully Integrated Voltage Controller. It's job is to generate the different voltages an Intel CPU needs more efficiently and more precisely. It does both of these but also has the innate side effect of making motherboard VRM designs much cheaper since they are required to supply a voltage of 1.8+V instead of 1-2V.  Now you may think that this makes no sense. However it is very simple what does 100% of all damage and heat generation in electrical circuits is current. By raising the output voltage of the motherboard VRM the VRM needs to supply a lower current and therefore can be cheaper or more efficient. For example if you need to deliver 250W(an OCed X79 or X99 CPU) of power to the CPU from the motherboard. With X79 the board would need to supply 185A at 1.35V with X99 it only needs to supply 138A at 1.8V. That is a 25% reduction in current requirements. The other thing that X99's FIVR achieves is that you no longer need and X+Y VRM phase setup so 100% of the VRM space available on the motherboard can be used to supply those 138A at 1.8V further reducing the strain put on each VRM phases by allowing for more powerful or more numerous phases.
Now lets go to absurd land. Lets say you want to run your new Haswell-e at 1.35V all day everyday until the CPU or motherboard dies. Well at 1.35V Haswell-e will easily be pulling 300-400W and because were in absurd land lets go with the higher of the 2 so 400W since you can probably still cool that with H2O. Now then 400W at 1.8V gives a current draw of just 222A or less if you push the VCCIN voltage higher. So now lets see how a 6 phase VRM like what you find on the eVGA X99 micro would do with this. Well 222A/6phases means we would have just over 37A of current per phase which should be no problem at all because even the 100$ GA-F2A88X-D3H that I reviewed has 40A phases. Now on a 6 phase you are pushing it rather close so I would recommend an 8 or more phase board for these kinds of OC endeavors especially if the manufacturer is a little too cheap to be true. However any quality motherboard with 8 phases will be fine.
Now I just need to buy an X99 board some DDR4 and a Haswell-e CPU so I can test what raising the VCCIN does to the Vcore and I can do a fuller writeup on minizing VRM load with Haswell-e.

This is the source for Haswell-e having a FIVR

No comments:

Post a Comment