Hi Abdallah
Go through the documentation to this forum http://docs.moodle.org/en/Performance first.
Then look for similar discussions here, for example "A moodle setup for 10K simultaneous users" http://moodle.org/mod/forum/discuss.php?d=111847 you can use the search facility built into Moodle.
Hardware and performance
Specifications Moodle Server 8000 user
This discussion has been locked so you can no longer reply to it.