READONLY - Copyright (c) 1985 by Paul R. Grupp

OVERVIEW:

    This program will set the disk system in a CP/M Version 2.x
operating system to read/only.  Once this program is executed the
only way to return the disk system to read/write is to do a system
reset (cold boot).  This "safety" is intended to prevent untested
software from changing any data on any disk.  This is useful even
if you know the software under test needs to write to the disk as
you can view the signon, menu, and any prompts until it does try to
write to the disk.  For example, if one of the menu options is to
display a directory, you can suspect that something is wrong if
this option tries to write to instead of read from the disk.  If
(and if when) a program does try to write to the disk a Bdos R/O
error message will be displayed and the program under test aborted.

THEORY OF OPERATION:

    When this program is executed it first checks to make sure that
it is running in a CP/M version 2.x environment and aborts if not.
It then determines the Bios jump table address for a disk write and
patches the Bdos R/O error address in place of the write address.
This will abort any program that tries to do a Bdos or direct Bios
disk write with a R/O error message, then warm boot.  Once the Bios
has been patched this program is terminated and no extra code is
left in place to maintain this R/O protection.  Also since the Bios
is not read in on a warm boot (only Bdos and CCP) this patch will
remain effective until a system reset is performed (cold boot).

USAGE WITH RAM DRIVE:

    A more attractive test environment may be achieved with the use
of a ram drive that has a program to "install" itself.  If the
READONLY program is executed before the ram drive install program,
then the ram drive will remain read/write while all the other disk
drives in the system will be read/only protected.  This would allow
programs to write to the ram disk for testing, still protecting
data on the rest of the disks in the system.








      (CP/M is a registered trademark of Digital Research)

                           Page 1 of 1