I had an AS/400 but unfortunately never got to run it on that. (it was a JD Edwards server for the ERP system)

Nope it was on good old winNT 4

I think we may have upgraded it to windows server 2000 at one point as well.

I remember that the disk partition it ran on ran out of disk space once.. it kept ticking along. just didnt let users make changes. Amazing stuff.