The standard of the time was to use open collector drivers for ttl level
signals. The pull up at the far end was typically between 220 and 1000
ohms. There was a world of machines that used this basic topology in
everything from external connections to fast backplane busses. There
were several terminating schemes for bidirectional busses, including
split termination with a 220/330 combination.

The IBM pc design team (the Boca Raton group) apparently misunderstood
the use of open collector logic. They chose totem pole active high drive
as their standard for irq lines, despite the fact that the universal
method was/is to use active low open collector lines. This fact alone
has caused a lot more problems in pc use than the printer port
definition.

-- Tom Rogers