Why does a PHP script use different amounts of memory on two servers?

Question

I have a fairly large webapp that I run on a Media Temple server. We have recently decided to move it to the Rackspace cloud. When I run get_memory_usage, I'm using about 4mb of RAM more, per page load. So I guess I have a couple questions.

1. Does it matter?
2. Why does this happen?

Answer 1

1. It can, if the memory limit isn't raised appropriately as well.
2. Additional extensions, or 32-bit versus 64-bit binaries/pointers.

Answer 2

Your Rackspace Cloud server is probably 64bit which will generally take up more memory.

Answer 3

It is most likely that your PHP configurations are different on both servers. The php configurations register_globals and register_long_arrays will use a little bit more memory because all Get/Post/Cookie are duplicated. Also some PHP modules will use more memory such as "Hardned-PHP" which isn't installed on all systems.