ORIGINAL: BigJ71
There are slight internal differences but the main difference is the P97is a single stack polymer frame pistoland the P90 is a single stack aluminum frame pistol.
X2
Ruger identifies their models "by year", hence, their first 9mm semi-auto pistol used to go after the government contract was a "P85".
Just so happens I built the mold for the plastic grips to that model year, also worked on the action, frame and trigger, these were wax injection molds used in the investment casting process...