Re: Green screen replacement. Was: Weigh in on Fast400 . . .

From: James W. Kilgore <eMail@James-W-Kilgore.com>
> Now I don't know the gory details so I'm just making up names as I go here
....
> let's say that a program that has a WORKSTN device in it causes the
compiler to
> include routines WSOPN, WSCLO, WSGET, WSPUT, etc. which is the necessary
code to
> have the program talk to the workstation controller.  What I am referring
to is
> a product that could be purchased, maybe, that would sit above the compiler
and
> substitute the above mentioned routines at compile time.
>
> These substitute routines would not talk to the workstation controller but
some
> other server program that runs in batch yet performs the same function.
Your
> application program would compile the same with or without the add on
product.
> ZERO CODE CHANGES!
>
> So if you don't have this product, you compile and use dumb terminals,
telnet,
> emulation cards, etc., but if you do use this product, you recompile your
> program and get rid of your dumb terminals and emulation cards.

A time-honored way of doing this is to recognize that WSOPN and friends
go through entries in the System Entry Point Table (SEPT). Make a copy
of the SEPT in your process, replace the entry pointers to WSOPN etc
with pointers to your own routines, and you are there.