com3 & com4 -> tty2 & tty3

[dpgerdes at osiris.cso.uiuc.edu]

/* Written 11:09 am  Apr 25, 1989 by dave at micropen in osiris.cso.uiuc.edu:comp.unix.microport */
>First, as usual, Mr Plocher is correct in that INT 2 is unusable for all
>PC/AT architecture machines (as opposed to PC bus.)  INT 2 is used to cascade
>a second PIC (Programmable Interrupt Controller) so that the extra interrupts
>the AT bus supports can be used.  Perhaps before "getting tired" of hearing

    Thanks for the information.  I never challenged whether he was correct
or not, but was merely expressing my frustration that every tech person
that has ever made a statement like the above to me has not been able to
justify it.  Maybe I should have used a better wording than "getting tired",
as it may have an unintended negative connotation against John.
    As for the remark about reading manuals, I have been through an awful
lot of DOS books looking for that information.   I have Norton's Programmer's
Guide in front of me and it goes so far to say: 
    "The reserved codes are 2, 8, 9, and 11 through 15" when talking
about hardware interrupts, again without explanation.