On Windows it's handled in Windows Update, and maybe there's a way to disable loading the new microcode. On Linux, it's explicitly provided to the kernel by whatever userspace you have. On Arch, for example, it's in a separate package called intel-ucode.
Some board firmware loads updated microcode when it's updated. It has to be loaded at each boot by software in order to change.
Some board firmware loads updated microcode when it's updated. It has to be loaded at each boot by software in order to change.