Magnum One/Magnum One (Mid-American Digital) (Disc Manufacturing).iso/d21/qtech527.arc/MULTI-T.TEC

Text File | 1991-05-29 | 5.7 KB | 121 lines

ID:MT Multitasking in DESQview
Quarterdeck Technical Note #152
by Stan Young

One of the features of DESQview is the ability to provide for the
multi-tasking or background processing of a program.  This feature
allows the user to start an operation which will not require user
intervention and then switch to another task while the operation
continues in background.

While multi-tasking is certainly a useful feature, it is important
to note that DESQview cannot provide multi-tasking all by itself.
A program's ability to multi-task in DESQview is dependent on the
setup of the program, the hardware being used, and in some cases
the way the program has been written.

What is absolutely required:

SETUP -  First, in order to multi-task a program must be set up so
that it is allowed to multi-task.  Under the default setup for a
program added to the DESQview menu by choosing the "Other"
selection from the Add A Program menu,  DESQview assumes several
things that prevent multi-tasking.

*  DESQview assumes the program "Writes directly to the screen."
*  DESQview assumes that if the program writes directly to screen
   and the machine is not a 386 with QEMM, it does not "Run in
   background."

Given that DESQview assumes that the program runs only in
foreground, under the defaults, the program will not run in
background even if otherwise capable of doing so.  Therefore it
is necessary to modify the default setup using "Change a Program"
to see if the program can run in background.  The first thing to
determine is whether the program actually "Writes directly to
screen" (see below).  If it does not, and you set the "Writes
directly to screen" option to "N",  DESQview will allow the
program to run in the background.

MEMORY -  Second, in order to multi-task a program must be able
to remain in active, addressable RAM.  Multi-tasking is an
internal function of DESQview, and DESQview does not REQUIRE any
add-on in order to multi-task.  HOWEVER, 640K can certainly be a
limited environment if you are trying to multi-task large
programs.  If you are planning to multi-task large programs, you
may need to purchase additional memory.

The only types of memory which currently can be used for multi-
tasking beyond 640K are EEMS memory,  EMS 4.0 memory ON A FULLY
FUNCTIONAL EMS 4.0 BOARD (an EMS 4.0 driver on old-style EMS 3.2
board will not suffice) or exTENDed memory on a 386 machine with
QEMM, CEMM or compatible 386 expanded memory driver.

If your machine's memory configuration is such that the program
must be swapped out to disk, ramdisk, or EMS or EEMS memory, then
the processing of that program will be interrupted.  You will
know this has happened if you get a "Swapping..." message when
switching from the program.  If this is happening and you have
configured your programs to minimum memory sizes, the only thing
that can allow you to achieve multi-tasking is to increase the
number or size of the addressable memory partitions available to
DESQview. As indicated before, this may require additional
hardware.

More information on this subject can be found in the DESQview
manual under the appendix, "Using Expanded Memory with DESQview".

What is usually desired:

SCREEN MANAGEMENT  -  Another item that is usually necessary for
effective background processing, although not absolutely
required, is for DESQview to be able to provide screen
management.

A program which actually "Writes directly to screen" cannot have
its screen output managed by DESQview.  Therefore, if it is
running in the background and updates the screen, what it writes
will print through on the screen of the foreground application.

Testing to see if the program writes directly to screen:

All graphics based programs write directly to screen; however if
your program runs in character mode, you should try setting it up
in a window that has the "Writes directly to screen" option set
to "N".  Then invoke the program, allowing it to come up in a
small DESQview window.  If the program loads into the window
without writing outside the window frame, the program does not
write directly to screen and should operate properly in the
background.  If the program does print outside the window frame,
the program does write directly to screen and you will have to
evaluate for yourself whether running it in the background would
upset your foreground operation too much.

On a 386 machine, Quarterdeck's QEMM 386 driver provides
virtualization of the screen in text, CGA, EGA, Hercules
Monographics, and VGA graphics mode so that programs using those
modes can run with their screens managed by DESQview regardless
of whether they write directly to screen or not.  If the programs
switch modes in background (for instance, switch from text to
graphics), you must explicitly set the "Runs in background"
option to "Y".

Keyboard and mouse handling:

Programs running in background should be well behaved with regard
to their use of the keyboard.  If they are not, running them in
the background may cause problems with using the keyboard in the
foreground window.  In some cases, setting "Keyboard Conflict" to
4 using Change a Program can alleviate this problem.

DESQview versions prior to 2.2 do not currently support the
background operation of a program that is using the mouse unless
that program is DESQview aware.  Running a program that uses the
mouse in background will cause the mouse to be lost for DESQview
or other programs.  As of version 2.2, DESQview "virtualizes" the
mouse so that non-DESQview aware programs "see" the mouse only
when in foreground.

        Copyright (C) 1991 by Quarterdeck Office Systems
             * * *   E N D   O F   F I L E    * * *