I just stumbled upon the Microsoft articles explaining about HotPatching. A facility in Server 2003 SP1 and above that lets admins install updates without rebooting. Doesn’t work for all updates, but could be used for a lot.
Put simply you just add “/hotpatch:enable” as a switch at the end of a downloaded hotfix and it’ll try and HotPatch instead of ColdPatch. If the hotpatch fails it will do a normal coldpatch.
It’s a really cool idea really. They just append the modified code to the end of the binary and tell the app that running in memory to use the new code. After the next reboot the modified binary get’s replaced with the proper updated version.