How can I find out what hard drive is in my iMac?

I'm sure I'm just missing this somewhere, but I can't find a listing for my hard drive (or any hard drive) on my iMac. I got an e-mail from Apple about the current hard drive replacement program, telling me that I have one of the defective 1GB hard drives. That settles it, right? Uh, not quite. Firstly, when I ordrered my iMac, I ordered it from the factory with a 2GB hard drive, NOT the std. 1GB. With me so far?....hang in there. Secondly, however, that hard drive subsequently croaked (just last July) and I had a replacement installed under Apple Care at a 'local' Apple store. Just a little farther... Problem is, they did not replace my 2GB hard drive with another 2GB hard drive, they replaced it with a 1GB hard drive. Maybe they thought I wouldn't notice, maybe they didn't know they had done it, whatever, I did not complain because I have never even come close to using 25% of the 2GB anyway. (deep breath) Sooo, how can I find out what kind of hard drive I have?

Thanks,

Rich 😎