That count has gone up and down in recent years, as much from mergers and acquisitions (where the AS/400 is often replaced with a Unix or Windows box, if one of the companies already has them) as from bad estimates.
Back in the summer of 1997, Bill Zeitler, then general manager of the AS/400 Division, said that the worldwide customer count for the AS/400 was about 275,000.
When IBM started the Green Streak discount promotion and was gearing up to do the second-generation iSeries revamp on the product (which started in January 2003 with the repackaging and repricing of the iSeries and which culminated in the eServer i5 announcements last summer and fall), IBM said that there were anywhere from 211,000 to 246,000 customers, depending on how you wanted to count uniqueness. Many customers have separate divisions with separate data centers.
According to the latest count from IBM, which was actually buried in the eServer i5 595 announcements in October 2004, the official OS/400 server customer count is over 245,000 customers, using over 400,000 AS/400 or iSeries machines.
