Thanks for your reply, Visvanath Ratnaweera!
You are right, when I test my system by 60 simultaneous users so that I see the CPU is consumed up to 95%. It made me anxiously about that. In my case, teachers can also upload videos in flash. Yet following thing that i read on moodle web. The moodle system will normally be consumed more than the CPU. I expect the help from you. Thanks a lot.