Threads and processes with respect to virtual memory

Hi,
I had a few questions regarding threads and processes in linux with respect to virtual memory.

1)does each thread use the MMU to start at Virtual Memory zero, or is that a process only concept.
2)if threads don't use the MMU, then can data pointers be shared among threads within a process.
3)if a thread is pulled out into its own process, then will we have a problem sharing memory pointers
4)what is the performance impact of having all processes instead of threads.

Please do let me know if anyone has any answer for these questions

Thanks & Regards
JAmes

I'll take two of those questions.

POSIX threads share the same address space. This improves performance, but it makes debugging difficult.

If your execution streams (for lack of a better generic term) communicate with each other very frequently or with great intensity, threads can help performance. Otherwise, stick with separate processes. It is very easy with threads to inadvertently do something silly, and silly in a complex way.

Hope this helps.