I'm not, but the reason I ask is because I've watched a lot of movies that feature the P89 and/or P90, and I don't know how to tell them apart. I've starred at pictures of each until my eyes are falling out of the sockets, and I spot no visual differences. The only difference I can see is when the magazines are ejected (the P89 is, of course, double-stack, while P90 is single-stack). That's how I was able to figure out that Skeet Ulrich's Ruger in "Jericho" was a P89. Otherwise, I never know the difference.
There are a lot of pages on IMFDB where I'm never sure which one's which. Can anyone help? Here are pictures for comparison:
KP89
P90
Usually, the way to tell a .45 apart from a 9mm counterpart (i.e. SIG 220 vs. 226) is the presence of the bulges on the frame, which indicate whether it takes a double-stack magazine. But Rugers don't even have that.