language design - What makes PHP slower than Java or C#?

Question

This is something I've always wondered: Why is PHP slower than Java or C#, if all 3 of these languages get compiled down to bytecode and then executed from there? I know that normally PHP recompiles each file with each request, but even when you bring APC (a bytecode cache) into the picture, the performance is nowhere near that of Java or C# (although APC greatly improves it).

Edit: I'm not even talking about these languages on the web level. I am talking about the comparison of them when they're number crunching. Not even including startup time or anything like that.

Also, I am not making some kind of decision based on the replies here. PHP is my language of choice; I was simply curious about its design.

Answer 1

One reason is the lack of a JIT compiler in PHP, as others have mentioned.

Another big reason is PHP's dynamic typing. A dynamically typed language is always going to be slower than a statically typed language, because variable types are checked at run-time instead of compile-time. As a result, statically typed languages like C# and Java are going to be significantly faster at run-time, though they typically have to be compiled ahead of time. A JIT compiler makes this less of an issue for dynamically typed languages, but alas, PHP does not have one built-in. (Edit: PHP 8 will come with a built-in JIT compiler.)