Indeed, isolates are similar to mod_php in that a small pool of shared processes can handle thousands of different applications simultaneously. PHP is truly gre

Indeed, isolates are similar to mod_php in that a small pool of shared processes can handle thousands of different applications simultaneously. PHP is truly great in that way! But just to clarify, mod_php isn't thread safe so parallel requests do not share memory, they each have their own process (prefork mpm). And for untrusted tenants you also need to combine with mod_setuid or mod_suexec for proper isolation, as PHP doesn't do any isolation of its own (they tried for a while but gave up, remember open_basedir?). In other words a server with 16GB of RAM could handle maybe 250-350 simultaneous PHP requests using mod_php, whereas I'm sure they can fit thousands of isolates in that footprint.