Originally Posted by
yoko1
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.
In the event that MCAS (or another system) is active the design is that trim signal from the yoke switches overrides* the system-derived input. The decision on which takes priority must be 'processed'. Ergo SOME processing power is involved and a processor, somewhere, is in line.
* I have used the word 'override' but I think 'cancel' might be better in the case of MCAS, or even postpone!