microcode updates are volatile - after a reboot the CPU is back to its programmed state. BIOS installs updates (which is why some CPU bugs are fixable by BIOS u

microcode updates are volatile - after a reboot the CPU is back to its programmed state. BIOS installs updates (which is why some CPU bugs are fixable by BIOS updates), and the OS can do this, too: Linux has drivers to update microcode on CPUs. The microcode files comes from Intel and are mostly incomprehensible blobs (see http://inertiawar.com/microcode/ http://inertiawar.com/microcode/)