The Boss OD-1 was about the first OVERDRIVE pedal made, exceptperhaps the Ibanez Overdrives. But the early Ibanez pre-tubescreamer OVERDRIVES were quite fuzzy and distorted, while the OD-1is the first of the "tube screamer type" overdrivepedals. It was in the very first series of the Boss CompactEffectors. The OD-1 came out in 1977 and was discontinued in 1985. They were very popular in the LA metal scene in the mid 80s and the Japanese scene in the same time and much longer. The SD-1 took over from the OD-1 in the mid 80s but people still wantedthat pure OD-1 sound. The OD-1 (and SD-1) use asymmetrical clipping, which Boss has a patent on, to give some thick overdrive with an edge. Tube Screamers use symmetrical clipping for a smoother, warmer, less edgy sound.