Yes I know. (On Unix that is. They are just "shared memory segments" on Win32 for example).

But it's not as beneficial as people think for perl processes, because "compiled" Perl code and Perl program data, are both RW memory to the perl executable. And even read references to perl variables can caused write accesses (and therefore COW) to the memory that holds them.

But the main point of my post is that ps/top will often, if not always, count the shared, readonly memory (the perl executable's code and RO data) against each process that shares it, which may be giving the OP a false impression of how much memory is consumed by his existing forking solution.