ID:PT Protection Level Explanation
Quarterdeck Technical Note #120
by Stan Young

Q: What is the "Protection level" field in Change a Program used  
   for?

Q: Why does my program run slower when I use protection level?

Q: Will Protection level "fix" my ill-behaved programs?

Q: What does Protection level do on my 286?

 Protection Level

The "Protection level" field of Change a Program can be changed
on any machine running DESQview, but only becomes active on 386
machines.

Protection level uses the paging capability of the 386 to trap
programs which perform operations outside of their normal memory
space or which use interrupts in unconventional and potentially
destructive ways.  Such operations could be considered
"ill-behaved," and might be symptomatic of programs which are in
the process of crashing the system.

Protection level has no ability to correct such ill behavior on
the part of programs.  It exists in order to protect the rest of
the system from a crashing program and to report on what the
program did.

It is also common that programs that generate "Protection" errors
are doing things that may be non-destructive and legitimate. 
DESQview has no way to evaluate the specific reasons why a
program may have written outside its memory space, only that it
has done so.  Normally, for programs that have proven to be
reliable, you should keep Protection level set to zero.  Higher
numbers, particularly 2 and 3, will tend to slow programs down
due to the overhead of trapping memory access outside the
program's partition.

Protection level is primarily provided for use with programs that
have proven to be unreliable while running in DESQview.  Setting
protection level for these programs should usually prevent them
from bringing down the system and the messages produced when the
protection error is trapped may serve to suggest to the developer
of the program what they might be doing wrong.

The specifics of the program operations that are trapped at
different levels of protection are proprietary to Quarterdeck,
but in general, the higher the number, the more "ill-behaved"
operations will be trapped and examined.

          Copyright (C) 1991 by Quarterdeck Office Systems