Hello all:

I'm new here and looking PHP these days, howerver , I'm confused by how it
works, and here is some questions I have.
Is there any old bird wanna help me out?

1. I heard there is a zend engine inside PHP playing the role as a virtual
machine, and PHP excution have 2 step, first compile to opcode and then
excute the opcode,
so is that means the php are compiled only once per file? or still need to
recompile when another request issued to the server? also I heard about the
caching extention about php, is it talking about caching the opcode? is't
caching the opcode or excute results? how it shares between the requests?

2. Is there some alternative choise except zend engineen, why need a zend
engine? for performance advantage or just easy for porting to different
platform?

3. Take linux apache for example, if compiled as a apache module, and using
prefork threading model, for example, if I have 100 process, is that means I
have 100 copy of PHP library local data(I assume only one reentrant
excutable image) in each process? compare to a worker model, like 10 process
and 10 threads in each one process, should it make a difference that we only
have 10 copy of PHP library local data ?

I'm not sure if this is the right place to talk about this, anyway, if you
know a better place, help me out :)
Thanks in advantage

Regards
Kai