Identifying HD in 700MHZ iMac

I purchased a used Graphite 700MHZ (summer 2001) iMac. It's supposed to have a 60GB HD. That's all that was available for the 700MHZ Graphite. After I installed 10.3 (to match my eMac) I noticed the "specs" in "About this Mac," say 20GB HD! I never knew how to find this information on 10.1. How can this be? Is there a way to tell if it was replaced at one time? Maybe by the serial #? It had very, very little use, so I find that unlikey though, plus why for a smaller HD anyway?

Noahsmom

You're right that this model had a 60 gb HD when new. As you speculate it could have had a disk failure and been repaired, maybe with available parts. It's also possible that the seller wanted to keep the larger disk so he swapped it for a smaller one.