'motherboard' etymology

[Maciej W. Rozycki]

On Sun, 28 Feb 2016, Jules Richardson wrote:

> > Computers existed way before 1980, and had many boards plugged into
> > wire-wrapped backplanes or motherboards.
> 
> Backplane was certainly a term from way back, I just don't recall seeing
> motherboard before somewhere around the 1980 timeframe. Maybe you're right
> though and it was in use too, but only by certain companies...

 FWIW I wouldn't call a motherboard a backplane and vice versa.  I'm not a 
native English speaker, but my technical background tells me these are 
simply different terms, at least as far as contemporary hardware is 
concerned.

 A motherboard in my understanding is a piece of circuitry which 
architecturally constitutes a computer system.  It may be lacking a direct 
way to connect a CPU or memory even, which may have to be plugged as 
daugthercards, one or more -- e.g. for a SMP or NUMA system -- and which 
may support different CPU architectures but the core architecture of the 
system itself, like buses, bridges between them, bus arbitration 
circuitry, maybe some essential peripherals -- it's all there, and in 
particular preventing daughtercards from operating on their own.  The 
majority of Intel x86 PC computer boards is a trivial modern example (and 
the computer boards of DEC DECstation and VAXstation lines is a classic 
computing example; some actually had their CPU on a daughtercard).

 A backplane OTOH is just an interconnect with no substantial circuitry, 
where it's the cards plugged in that constitute the system or systems.  
The interconnect provides a way for cards to communicate between each 
other, but the core architecture of the system is on one or more of the 
cards, which in some cases may be able to fully operate on their own, 
without a backplane present.  A modern example is CompactPCI (while DEC 
Q-bus backplanes are a classic example).

 I gather there's some room for debate around some border cases, however I 
wouldn't ever call an x86 PC computer board a backplane just as I wouldn't 
call a CompactPCI backplane a motherboard.

  Maciej