Zamin_ :
720p and 1080p videos not play play slowly .why?? my system is pentioum 4 2.87ghz 2 gb ram
I'm guessing you are saying your HD video play slowly. Because your computer is too slow to run them. Adding a video card and another 2 GB of RAM may help, but for that price you can buy a used Core 2 Duo system that would be faster overall. If these are online videos, it may also be a slow internet connection.