Just for completionism, two decades back the absolute smallest zSeries was a "rolling box", low and squat, that just barely fit into an office building elevator

Just for completionism, two decades back the absolute smallest zSeries was a "rolling box", low and squat, that just barely fit into an office building elevator. Think of a short rack tipped on its side with wheels, but all a single computer. IBM loaned us one to port our Linux software to it. Normal zSeries are like a custom rack to multiple racks, except again all a single computer. The smallest iSeries I've seen was essentially an "oversize tower PC" form factor.