I read on the Internet the Seagate 1TB ST31000340AS driver default to 1.5 Gbits because there is a jumper..Is that true??
 
I look on the jumper block and there is a jumper on right side..How do I remove this jumper (enable it to 3.0 Gbits)? It look very small and deep inside.
 
Thanks!

Yes this jumper is to make the drive 1.5Gb, I use a tiny flathead screwdriver but I have also used a razor blade knife too.  Although if its just 1 drive in the system the jumper will make no real difference.  It will make reading from the cache on the drive a tiny bit faster.  Seagate also disables SSC (spread spectrum clocking) on the drives from the factory.  If you want to play with that search for SSCSET.EXE on the web.

Thanks for your reply..so u saying if I remove the jumper..The drive will be a bit quicker? I am only using the PC for regular tasks like surf Web, watch movies and occasionaly video editing.....and not something intensive such as video games or intensive hardisk operation such as server.
 
Currently my system is using 2 drives..1st is a WD 500GB (OS+data) & 2nd is Seagate 1TB (data).
 

Technically it would be quicker but its not anything you would notice.  For your situation I would leave it as is.  Seagate jumpered the drive that way to make it more stable/compatible with various controllers.  

The jumper is there to limit the drive to 1.5 G/bs transfer rate (The original SATA speed) in case that is what your drive's controller is designed for.  If you know that your system can handle SATA II drives properly (i.e. 3.0 Gb/s peak transfer rate), just pull the jumper off.  It pulls straight off with a fingernail, tweezers, small needlenose pliers, knife blade - whatever works.  You do NOT need to put it back on a different set of pins.  If it suddenly fails to work, then likely your system does not use SATA II, and you would have to put the jumper back on the original pins.

I have the same HDD. I pushed the jumper down. Isn't this the same, as taking it off?

The jumper is a little plastic block with springy ontacts inside that slide over two pins, connecting them together.  Merely pushing the jumper farther onto the pins changes nothing.  To disconnect the pins (and make the drive function at the faster speed) you must remove it completely.
 
Some drives actually have "do-nothing" pins in the jumper block, so you can store the little jumper by pushing it onto a pair of pins that does nothing.  However, most drive makers do not tell you where the "storage position" is, so you're better just to remove the jumper and keep it with you myriad spare parts.

Thank you, I will do this