I'm not sure if I'm remembering from the Franz Joseph tech manual or some other early Trek book but I recall a phaser having various settings:
- Stun: make a living thing dazed
- Heavy stun: make a living thing unconscious
- Kill: make a living thing die
- Heat: speeds up molecules, things get hot
- Disrupt: separates molecules, blows things up
- Dematerialize: energizes molecules, make things vaporize
Also used during TOS were a wide stun beam for dealing with a crowd and an invisible cutting beam. There is also one use of a stun setting on the ship mounted phaser banks.
I'm not clear on whether the phaser is just outputting varying power levels of the same energy beam or is each setting a different beam or stream of different particles?
What other or different settings do you think were on the TOS phasers and how did the later series or movies differ?