Originally Posted by
YYZjim
Perhaps the better question is this: When a pilot presses his yoke trim switch, does that action immediately energize the trim motor with current? Or, instead, is the pilot's action routed as an input to the trim computer, which actually controls the voltage applied to the trim motor? The difference could be fatal if the computer is too busy with other things to process the pilot's command first.
YYZjim
As far as the main electric trim (activated by the yoke trim switch), it's all switches and relays as far as the electric part of it goes. No computers needed. Keep in mind that the basic 737 design goes back 50 years, so Boeing figured out how to do a lot of things without IC chips. There have been updates along the way, of course, but the main electric trim system is pretty robust and reliable.
The automatic trim inputs (Speed Trim, Mach Trim, Autopilot) are a different matter.