Yes, but I'm not sure about mod_perl..
For every hit your server gets, another instance of perl is started (so that it can execute the cgi file that the user requested)..
mod_perl and php are both run from the apache server level, and a new instance isn't started for each hit you get. Everything is already there and running..
That probably helps free up quite a bit of memory for the server when you have a heavy load also.
I'm sure there is a bunch of other stuff too that I don't know about.. I just know the basics of it :\
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Jeremy 'PeelBoy' Amberg