Maciej W. Rozycki
macro at linux-mips.org
Mon Feb 29 09:58:28 CST 2016
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
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.
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