"BI" fonts can, it seems, largely be traced
to the impact
of PostScript
There was no room for BI on the C/A/T. It appeared in
troff upon the taming of the Linotron 202, just after v7
and five years before PostScript.
Seventh Edition Unix shipped a tc(1) command to help
you preview your troff output with that device before you
spent precious departmental money sending it to the
actual typesetter.
Slight exaggeration. It wasn't money, It was time and messing
with film cartridges, chemicals, and wet prints. You could buy a
lot of typesetter film and developer for the price of a 4014.
Doug