This is rather off-topic for FAQ-maintainers, but: I believe that
the reason the "gecos" field was added to an early Unix system's
passwd file was to contain a user's login information on the
local GECOS system. The Unix system had no printer, or it had an
inferior one, so a scheme was rigged up so that print jobs were
routed to the GECOS system, and printed under the corresponding
user's account there. In other words, that early Unix system
used GECOS as its line printer.
Steve Summit
scs@eskimo.com