<I'm wondering: was the IBM PC the first machine with PSU in the rear
<right, drives in the front right, motherboard in rear left, or did they
<borrow this design from someone else?
I don't think it was borrowed as much as there are few choices when
you put most of the meat on one card. Packaging hardware is an
older art than the PC.
Personally it was a horrid layout with poor airflow for cooling.
Allison