i read somewhere
I read somewhere that the earth is flat - it must be true. Please cite your sources.
thread safe is for multithreading
This is non-sensical
and is faster
Possibly true depending on a large number of other factors.
shldnt php just release a thread safe php?
PHP has been thread safe for a very long time (approx 10 years now). You may be refering to the issue that Rasmus Lerdorf pointed out some time ago, that adoption of thread-safe code by third-party developers (i.e. extension writers) was expected to lag behind PHP's adoption. It is not known whether this is still the case.
This new FastCGI handler from Microsoft
You seem to be under the impression that this amazing new invention by Microsoft (no, just a new release of software originally designed by someone else) can somehow seperate the threadsafe and non-threadsafe parts of the php installation - this is not the case.
putting twin turbos on your car
I expect it feels like that compared to the alternatives on MSWindows.
so can i say if i use iis, i should use non thread safe php and thread safe for apache?
This sentence does not make any syntactic sense. Certainly for production systems, unless you have reason to believe that the system may be thread safe, then you should not use a threaded PHP module. And for Microsoft NT / Solaris / AIX systems then there is a performance beneift in using a threaded apache. For Linux systems the difference between threaded and pre-fork is significantly less. Not sure about BSD / Apple.