precaud wrote:I wasn't aware that BIOSes set the vreg based on stepping codes.
Just to clarify, I don't think the BIOS has any involvement in this function.
The VID is a binary sequence of high/low voltage levels on a few pins (5 in this case) from the CPU. The CPU package is hardwired to set each of those pins to either a high or low state, forming the VID.
Those 5 signals are routed to the voltage regulator IC, which then outputs the corresponding voltage to power the Vcore rail. This should work even with no BIOS present.
BIOS support comes into play for setting up the software side of things like initializing registers or whatever (not sure exactly what it needs to do).
I don't know how the voltage regulation works on boards that support tweaking the voltage though. In those cases, I guess the BIOS is modifying a reference voltage somewhere to trick the regulator.