 The Sol-20 remained in production until 1979, by which point about 12,000 machines had been sold.By that time, the "1977 trinity" —the Apple II, Commodore PET and TRS-80— had begun to take over the market, and a series of failed new product introductions drove Processor Technology into bankruptcy.Felsenstein later developed the successful Osborne 1 computer, using much the same underlying design in a portable format.