I heard that threads in perl [...] cannot utilize multi-core

Perl threads certainly can use multiple cores.

How perl based websites handle multiple requests at the same time without threads?

Most of them probably use multiple processes.

How can perl threads use multi-core? can you tell me more in detail? and how perl's ithreads work exactly?

Perl uses kernel threads; under linux, those kernel threads are pthreads.

---

With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.

"Science is about questioning the status quo. Questioning authority". I knew I was on the right track :)

In the absence of evidence, opinion is indistinguishable from prejudice.

I'm with torvalds on this Agile (and TDD) debunked I told'em LLVM was the way to go. But did they listen!