Remember the fully integrated voltage regulator ( FIVR) introduced with Haswell CPUs? Turns out that news of Intel axing the technology was not completely true. Intel's previous FIVR was implemented to reduce motherboard voltage regulator (VR, VRM, or MBVR) complexity, as it fed the CPU a single voltage and the CPU then internally branched off, reduced, and controlled the other voltages needed for other CPU domains (graphics, system agent, cache, IO, etc.).
Traditionally, CPU voltage regulators are fed 12v from your main system power supply, and then they reduce it down to voltages below 2v for the CPU and its different domains. However, as CPUs became more complex they required multiple separate VRs, each with their own controllers (PWM Controller). Adding more external VRs not only increases motherboard costs because of the need for each VR to be individually controlled, but also more importantly, it takes up motherboard real estate which is scarce on a motherboard with eight memory DIMMs surrounding the CPU. Over the past week, Intel quietly made public volume 1 of the Skylake-X datasheet, and you can find it here: Intel Skylake-X Datasheet Volume 1 of 2.
In table 1-1 on page 14 we find that "IVR" will be referenced in the datasheet, and it stands for "Integrated Voltage Regulation (IVR): The processor supports several integrated voltage regulators." Later in the datasheet we find reference to the fact that the IVR is related to the previous FIVR through a signal name called "FIVR_Fault", which "Indicates an internal error has occurred with the integrated voltage regulator. The FIVR_FAULT signal can be sampled any time after 1.5 ms..." We then learn further down about the VCCIN signal, "1.8 V - 1.55 V input to the Integrated Voltage Regulator (IVR) for the processor cores, lowest level caches (LLC), ring interface, PLL, IO, and home agent. It is provided by a VR 13.0 compliant motherboard voltage regulator (MBVR) for each CPU socket.