[Freedos-user] parallel port question

[coralline algae]

I was asked recently to look at a problem with a new pc (hp) and an application
they had installed which was not able to print forms on a line printer

the application as it turned out was dos based, i tested the printer with
lpr which worked ok

after a support call to the vendor, they asked me to check the bios mode settings
for the parallel port and the options were  ecp, epp and bidirectional.
At that point the vendor said oh sorry you need to buy one of our pc's as
we only support  spp mode and we can supply that pc hardware.

As a sanity check I looked at the bios for a few other pc's and not one had spp as a bios option.

Can anyone explain how a dos program could be coded to depend on
a bios feature of the parallel port ?

Thanks and sorry if too far afield