DOS is a playable word

do Scrabble® Dictionary

noun
pl. dos
the first tone of the diatonic musical scale
verb
did or didst, done, doing present sing. 2d person do or doest or dost 3d person does or doeth or doth
to begin and carry through to completion
7 Playable Words can be made from "DOS"
   2-Letter Words (4 found)
   3-Letter Words (3 found)