Category : Alternate Operating Systems - Quarterdeck DesqView, CP/M, etc
Archive   : QTEC9306.ZIP
Filename : PROTECT.TEC

ID:PT Protection Level Explanation
Quarterdeck Technical Note #120 Filename: PROTECT.TEC
by Stan Young CompuServe: PROTEC.TEC
Last revised: 2/12/92 Category: DV

Subject: A discussion of the Protection Level field on the second page of
DESQview's Change a Program Menu; what the settings do and don't do.


Q: For what is the "Protection level" field in Change a Program used?
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 as a diagnostic tool for use with
programs that are having problems running in DESQview. The Protection Level
feature may report a useful error message that will help you try to figure out
why the program is failing. 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. It is not useful to
have Protection Level set above 0 during the normal running of any program.
Almost any program can force a protection error to be reported at level 3
eventually, and programs that have no trouble running in DESQview can be
caused to have problems by setting Protection Level above 0.
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.

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*This technical note may be copied and distributed freely as long as it*
*is distributed in its entirety and it is not distributed for profit. *
* Copyright (C) 1991-2 by Quarterdeck Office Systems *
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