While working as a DJ we used reel-to-reel tape recorders to play commercials and promos.
Today, I suppose all of that is on CDs or something similar.
And BTW, we actually had live people running the station. Today, there are no announcers, just computers which play the music and commercial CDs and in the case of national talk radio, the entire process is automated as the local station’s computer turns the network on and off.
I do know they have DJ’s at least at one station, WONE 97.5 in Akron, OH. I went to school with the evening drive-time DJ.
I should ask her if she actually chooses the music and plays it or if she just talks between songs a little.