On Mon, 29 Feb 2016, John Willis wrote:
FWIW, the IBM term for "motherboard" was
"planar", at least in the era of
the PC, PC/XT, PC/AT, etc.
I believe I saw it on Lenovo ThinkPad part lists some 5 years ago, so the
term must have survived well beyond the PC/AT, etc.
Maciej