'motherboard' etymology

[Maciej W. Rozycki]

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