/FHQ9:  I've heard that DESQview does preemptive multitasking.  What does that
mean?/FB



Let's say you have one toy (the 80x86 processor in our case) and 5
children (5 programs that you want to run under DESQview
simultaneously).  There are two ways that Dad (DESQview) can let each
child play with the toy.



/ML4//CH(1)/CN Dad gives the toy to one of the children, who plays with it until
she gets bored.  Then she returns the toy to Dad, who gives it to one of
the other children.  This repeats until all the children have played
with the toy, and then Dad starts over with the first child.



/CH(2)/CN Dad gives the toy to one of the children, and starts a timer.  If
the child gets bored with the toy before the timer expires, she gives it
back to Dad.  However, if she still holds the toy when the timer
expires, Dad reminds her that good children must share, and takes it
away from her.  He then gives it to the next child and restarts the
timer.  When all the children have played with the toy, Dad returns it
to the first child. She continues playing with it where she left off.



Sometimes one of the children may want to take the toy apart. Since none
of the other children wants to play with a disassembled toy, the child
will request that Dad not take away the toy until the child says he can.
In that way, the child can re-assemble the toy before any other child
gets it.



/ML-4/The first method is called ``non-preemptive'' and conversely, the second
is called ``preemptive''.  It is generally agreed that preemptive
multitasking is much better because one program cannot accidently
``hog'' the CPU.  One of the major technical differences between
DESQview and Windows is that DESQview preemptively multitasks all
programs, while Windows does non-preemptive multitasking of Windows
applications.



When a program running under DESQview calls a DOS or BIOS function, it
effectively ``disassembled the toy''.  DESQview recognizes this and
temporarily suspends any other program that attempts to make a DOS or
BIOS call until the current DOS or BIOS call ends /JB(see Q10)/q10.txt/.



DESQview-oblivious programs /JB(see Q3)/q3.txt/ can act like selfish children when
they are waiting for keyboard entry.  Even though they aren't playing
with the toy, they keep hold of it.  Shareware and freeware programs are
available for forcing these programs to share the toy /JB(see Q24)/q24.txt/.