Apache 2.x has been released for a long time, and it is recommended to use 2.x in many cases instead of 1.3.x.
However, in the official manual in PHP, it is clear that:
WARNING Do not use the combination of Apache 2.0 and PHP in enterprise applications or WINDOWS.
Why is that?
This discussion can explain some questions http://simon.incutio.com/archive/2004/03/31/phpandapache2
Generally, Apache 2 can be compiled into a multi-threading mode, while some of the PHP's stuff is not THREAD-SAFE, so it is not recommended to use Apache in Multi-Threading mode. In other words, if the Apache2 is compiled into a multi-processes mode, PHP should work properly. As for the Apache2 working efficiency under Multi-Processes, what should I don't think about it compared to 1.3.x?
Specially mentioned in the Manual in PHP:
If you want to compile a multi-thread version of Apache 2.0, you must overwrite the standard MPM-Module Prefork, or Worker or Perchild. To be this, you need ... Use --with-mpm = worker or --with-mpm = perchild option. You need to know what you are doing. For more information, please refer to the part of the MPM-modules in the Apache document.
Note: To compile multithreaded version of Apache, your system must support multithreading. This also means that PHP is needed as Zend Thread Safety (ZTS) that is in the test phase. Therefore, not all extensions can be used. Recommended Compilation Apache Using Standard Prefork MPM-Module.
Well, let's go see ZTS. Also, I don't know how PHP5.
