[carol m]

If you want a USB connection you should check that the RP90 works like that - when I was checking, only the RPx50 models had usb eg RP150, RP250. RP350. I'm not sure how the non-usb pedals connect with the computer, probably through your amp but make sure your connections are what you want before you buy.

Also the higher number models just have more ' pedal voices' to choose from as far as I know, and don't follow a progression of time.

If you don't get your pedal, you can always use the many fx options (equiv of pedals) supplied in the free software recording interface called Reaper. Reaper can be quite daunting at first if you have no experience with a simpler recording interface, but the basics are all the same for all those programs like Audacity (also free but not really any pedal type effects in the program itself).

With Reaper you can plug your guitar into your computer link, change the Reaper effect (fx) you have chosen and hear the result in real time. There are tutorial videos for it online and there are some others provided on this site by Tekker in the Lessons from Members section of the free lessons.