Star Trek: 10 Things You Didn't Know About Phasers

Phasers and disruptor weapons differ in several key ways.

For starters, a phaser can be set to stun, whereas a disruptor is a purely lethal weapon. This difference was an easy way to show the contrast between the violence of alien empires like the Klingons and the comparatively humane Federation.

Also, as mentioned earlier, phasers fire pulses of fictional particles called nadions, whereas disruptors seem to be much blunter, simply disrupting the molecular bonds of their target, and while both phasers and disruptors are capable of disintegration, disruptors often do so in a much slower and more painful way.

However, Starfleet still used disruptors occasionally. In the Original Series episode Obsession, we learned that type 2 Starfleet phasers actually have a mode called the 'disruptor-B setting', suggesting those specific weapons combined both phaser and disruptor tech.