mike wrote:

Perhaps that's the confusion. Loaded at boot is volatile.

Technically I suppose microcode loaded by BIOS is volatile too, the CPU
wakes up with the factory microcode, the BIOS immediately updates it the
microcode stored in flash, and possibly the O/S updates the microcode
again if it has a later version than the BIOS does.

The CPU is never permanently updated with newer microcode.

The word "update" implies, to me, a non-volatile fix/patch that needs
to be done once. So, we're overlaying the the microcode
that the BIOS loaded
at power up with microcode that the OS provides??
That gives me more confidence that the "update" won't bork my BIOS.
It shouldn't have to do anything with the BIOS.

If you somehow end up with bad microcode in your BIOS flash, which the
BIOS always gives to the CPU at power-on, you've no way out unless you
start removing flash chips and replacing them.

At least if the microcode is updated by the O/S you can boot from
different media if you need to ...