Hot start is one of 2 normal Production starts. If Menu - System - Config, Use Hot Start is set to TRUE, then the robot can resume its task when power comes back on. The robot will “remember” what was happening 8 milliseconds before the power was lost. If the physical robot body’s position is within its “resume tolerance,” which is likely, the robot will move slowly to re-acquire its interpolated program path, and then speed up to the override speed set in Menu - Setup - Cell, resume speed.
Cold start is the other of the 2 normal Production starts.
If Menu - System - Config, Use Hot Start is set to FALSE, then the robot will power up on a Cold start when power returns. Think of a Cold start as a Hot start with a FCTN - Abort thrown in there. The robot will have forgotten its program stack upon power up, and so the task it was doing when power was lost cannot be easily resumed (unless you understand very well how to rebuild the program stack.)
A Cold start is also the only way to exit a Controlled Start, and must be done, in that case, using the FCTN key (or wrench key), Fctn - Start (COLD)
Controlled Starts and Boot Monitor (BMON) starts are ways to... shall we say... fool around with the robot’s memory ( change memory settings or add software or prepare the robot’s memory to restore a backup.)