Originally Posted by The Golden Boy

From 1976-1985 Trek's hierarchy was pretty simple. There's a few deviations here and there- but it's all pretty easy.

A 200 or 300 level frame was usually HiTen frame/fork (differentiated by the dropouts)
A 400 level frame was usually a Mangamoly or CrMo with a HiTen fork and stays
A 500 level frame was usually a CrMo frame with CrMo fork and stays
A 600 level frame was usually Mangamoly or 531 frame with CrMo fork and stays
A 700 level frame was 531 frame/fork
A 900 level frame was Columbus frame/fork.

In the early days, the TX bikes were all "touring" or "sport" (or "regular ol' bike") geometry but the TX900 was a racing geometry.
(the "x" stands in for the tubing designator ^)Shortly after, the x10 level frames were "sport" (or sorta "sport touring")
The x30 x60 and x70 frames were "racing" geometry
The x20 frames were "touring" geometry- usually with cantilever brakes.

Again, there are little deviations here and there- but that's it in a nutshell... So, roughly, the higher the bike number, the more prestigious it was. The Columbus tubed bikes were more prestigious, so the 9 is pretty much "top of the line." The HiTen models were the entry level and carried a 200 and 300 designation.