If I just fork() them, will these process be able to run in parallel on separate processors?

Yes. For fork(), the limit is 64 pseudo-processes on the Windows platform; $^O eq 'Win32'. There's no limit using threads.

> I have a six processor win10 system and I have a very CPU intensive program that I can easily carve into parallel processes

I advise you to stay away from Perl's fork emulation on Windows, too many surprises and general weirdness. There are better alternatives. If you provide more detail on the specific problem you are trying to solve, we will be able to better advise you.

In case it's of use, I keep a list of general references on this topic: Threading and Concurrency References

Update: I see from my list of references that you asked a similar question last year: Parallel processing on Windows ... and another one earlier this year: fork() on win10. It would have been nice if you'd mentioned that in your post and told us what you've tried from the responses to those threads ... and told us more about your CPU intensive program.

Yes, it creates a real thread, which can be assigned to a different CPU by the OS.

BUT! You'd be better off avoiding the very poor emulation of fork. This could be done, for example, by using threads directly.

> I have a very CPU intensive program that I can easily carve into parallel processes

Please tell us more about this program:

• Did you write it yourself? Do you have its source code?
• What language is it written in? How many lines of code?
• What do you use it for?

a situation where I would want my program to duplicate itself in memory and start doing the exact same thing twice ... I don't see why it's necessary or useful

The point of fork is not really for the parent and child to do the exact same thing. If you look at its documentation, you'll see that the parent and child get different return values, allowing them to follow different code paths. Typically, the parent will fork multiple children and then manage them, while the children will be doing various tasks. This scheme is widely used in many web servers, see e.g. preforking server. For just two examples of many in Perl, see Parallel::ForkManager and Net::Server.

For example, certain calculations could profit from it if one distributes them on several CPUs. What else do you have the expensive gizmos for? Here is a simple, admittedly somewhat pointless example:

#!/usr/bin/env perl

use strict;
use warnings;
use Math::BigInt;
use Parallel::ForkManager;
use Time::HiRes qw ( time );
use feature qw(say);

my $sleep_period = shift;
my $processes = qx(sysctl -n hw.ncpu);

chomp $processes;

my $pm = Parallel::ForkManager->new($processes);

$pm->set_waitpid_blocking_sleep($sleep_period);

say qq(processes: $processes);

my $start = time;

for my $number ( 1 .. 50 ) {
    $pm->start($number) and next;
    my $factorial = Math::BigInt->bfac(2000) for 1 ... 10;
    $pm->finish(0);
}
$pm->wait_all_children;

say qq(fork: ), time - $start;
[download]

See also this eight-year-old thread from which the example comes.

«The Crux of the Biscuit is the Apostrophe»