Origin of 'Straight 8' name

[John Ames]

I'd definitely be interested to hear if the DECheads on this list know
the specifics, but I'd gathered that it came about once other models
were introduced and the need arose to differentiate between, say, a
PDP-8/e and a "straight" (i.e. vanilla) PDP-8. The car connection
probably made the particular phrasing happen (of course, they
originally photographed it in a Volkswagen, but they couldn't very
well have started calling it a "flat-4!")