The most common Mac mini rack mount enclosure holds 2 minis in 1ru. I think at amazon's scale they could probably get 4 minis in 1ru with some custom cooling.
how dense do you think instances are on average in the amazon datacenters?
19 mod 7.7 = 3.6, 3.6 x 1.4 = 5.04 in^2
Presumably the greater waste of bottom side down is in higher number of shelves?
That sounds wasteful to me. Is that really the most common way for mac hosting companies to do it?
There's an image there that appears to have the units mounted sideways for perhaps 6 minis in 2 RU?