Does PHP have an inherent memory limit, beyond what I set?

Does PHP have a built-in limitation on how much memory it can use? In other words, if I have a machine with many gigs of RAM and change php.ini to allocate most of them, will scripts still hit some开发者_开发知识库 lower limit?

(If you're curious, the goal is to run an automatic documentation generator, written in PHP, on a very large PHP code base.)

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PHP will consume as much as it has, this depends on your operating system. You can not extend the memory limit of PHP beyond what your OS has to offer.

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Apart from the PHP ini directive memory_limit you are only bound by the machine's available RAM. Note that memory_limit is per script, so running multiple scripts at the same time can eventuall sum to more memory than you server has.

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The maximum amount of memory per process can also be limited by the operating system and/or some configurable resource limits.

E.g. on a windows system a 32bit process is limited to 2/3/4 GB memory per process (depending on whether you use a 64bit version of windows and the setting of IMAGE_FILE_LARGE_ADDRESS_AWARE). A 64bit process might be limited to 2GB as well (with IMAGE_FILE_LARGE_ADDRESS_AWARE cleared).
On a linux system there are similar restrictions and often limits set via ulimit.