This is the 16 GB G.SKILL Ripjaws X DDR3 kit I have:
Paired with “Haswell Refresh” i5-4690k and it’s “Fully Integrated Voltage Regulator” (FIVR)
With the CPU at all stock settings, I spent a good part of the day messing with memory timings, clocks, and voltage. With only a single DIMM populated to test each 8 GB stick separately. My findings were astounding. To my surprise this RAM kit overclocks very well. Not even just enabling the XMP-1600 profile - but going beyond 800/1600 MHz. I had Windows 10 booting at 1400/2800 MHz DDR3 reaching write speeds of 8 GB/s (be it with many errors however). I didn’t try anything higher because it was unstable.
After messing with the various UEFI settings all day I came to the conclusion that this was just the little PC3-12800 that could.
I was hesitant to go over 1.70 V, so then I started to get very interested in DRAM overvoltage safety. I stumbled upon some findings saying you can damage your CPU by just only overvolting the sticks of DRAM. Damage my CPU?! WHAA - BACK TO 1.50 V!!!
I found that there are a couple separate voltages running to the memory and that the main one used in overclocking is the VDDQ - which is the supply voltage for the output buffers
Most DDR memory devices use a common supply voltage for core (VDDQ), I/O (VDD) and logic (VDDL) voltages, commonly combined and referred to as simply VDDQ
DDR memory’s VDDQ voltages is the simplest supply rail
While VDDQ can typically be supported by a conventional converter, it generally requires pre-bias support and the ability to regulate through high-speed transients as the memory switches states.
So this leads me to some findings saying the CPU regulates the voltage provided to the DRAM. I’ve never heard of this before and I was shocked. I know starting with Intel 4th gen (Haswell) they moved the voltage regulation onto the CPU die & package - calling it FIVR. I thought the FIVR only managed the voltage for the CPU. Obviously that would include the Integrated Memory Controller (IMC). The IMC is on the CPU and is separate from the voltage the actual sticks of DRAM get.
As for CPU overclocking - from what I’ve read, people recommend setting the FIVR input (Vccin) to 0.40 V higher than Vcore. So at default that’s usually 1.80 V - only 0.30 V higher than DRAM voltage of 1.50 V for DDR3. What’s the relation between DRAM voltage and Vccin?
Back to the question at hand here - is it true that the FIVR provides the voltage regulation for the DRAM sticks. If so, why are there separate VRMs next to the DIMM slots on some motherboards. Wouldn’t the motherboard only need a single main VRM solution to provide for the FIVR?