Alternative PHP Cache (APC) project is free and open. It optimizes PHP code and caches data and code in the shared memory. The project home page is http://pecl.php.net/package/APC where you can download its source code. Binaries that you can download from this site are built from official releases of APC and PHP. The only added thing is the version info sheet for dlls.
You can find the documentation on the page http://www.php.net/manual/en/book.apc.php.
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