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From: n8541751@unicorn.cc.wwu.edu (Where there is darkness, light)
Newsgroups: comp.os.msdos.programmer
Subject: Re: TSR's - Must they be converted to .COM?
Keywords: TSR
Message-ID: <1991Feb16.061311.22010@unicorn.cc.wwu.edu>
Date: 16 Feb 91 06:13:11 GMT
References: <3188@unccvax.uncc.edu>
Organization: Monkey Tree Computer Services
Lines: 31

cs00chs@unccvax.uncc.edu (charles spell) writes:

>If TSR's must be converted to .COM, why? I know that there are some .EXE
>files launch a TSR, how? Thanx in advance.

No, TSR's don't have to be converted to .COM files.  Usually it simplifies
programming though, because well-behaved TSR programs must follow certain
unofficial rules, such as using their own built in stack, in order to
be universally successful.  Limitations such as this make the use of
a single segment very convenient, thus the traditional way of writing
a TSR is in assembly language, using a .COM organization.

One of the most common TSR programs is the installable DOS device driver.
This had to be a .COM file until DOS 3.0 arrived, with the capability to
load an .EXE format driver.  Most programmers, myself included, still
write these as .COM files to remain compatible with older DOS versions
which are unfortunately still in use.

A good book which explains this subject further is:

DOS Programmer's Reference by Terry R. Dettmann, QUE books,
ISBN0-88022-327-8, LC 87-60811.

It also has much other information, including undocumented DOS functions,
critical to writing TSR's.

Kris.
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