Q40408: Setting the Overlay Interrupt (/O) in LINK

Article: Q40408
Product(s): See article
Version(s): 3.61 3.65
Operating System(s): MS-DOS
Keyword(s): ENDUSER | docerr | mspl13_basic
Last Modified: 20-JAN-1989

Question:

Page 272, Section 12.2.12, of the "Microsoft CodeView and Utilities
Software Development Tools for the MS-DOS Operating System" manual
states that you can change the default overlay interrupt. The default
interrupt is 3F hexadecimal. Is the manual correct? Do you have to
change the interrupt if you have a program that uses overlays and it
spawns a program that also uses overlays?

Doesn't the compiler save interrupts? Suppose both Programs A and B
use overlays and A spawns B. If B is a Microsoft C Version 5.00 or
5.10 program, shouldn't it restore the original INT 3F address when it
exits? Thus, everything should work correctly without
/OVERLAYINTERRUPT.

Response:

You are correct; the C Versions 5.00 and 5.10 compiler saves and
restores the interrupt so there should be no conflict. The C Versions
5.00 and C 5.10 manual is incorrect. This switch need only be used if
you are linking a program with overlays, and INT 3F is being used by
something else when you run the program. For example, INT 3F might be
used to communicate with a hardware board or a TSR might use it;
however, this is unlikely.

This option is for advanced users who know their configurations well
enough to know who is using which interrupt vectors and know there is
a conflict.