The stock 5050 is a 1/2 track record and playback machine. Most models (with 4 heads) will also playback 1/4 track stereo so you can playback prerecorded tapes on both sides (flipping the tape over positions the other 2 tracks over the same part of the head that played the first side).
I suppose you could have the record and erase heads switched to 1/4 track (it would probably require some other parts too but the heads would be the expensive parts).
If you want more explanation of track formats and tape recorders in general, there's a sticky at the top of the General Forum which is a beginners guide. It contains tons of info about reel to reel tape.
