When I copy the files from one driver to another(internal drivers), copying speed is between 13-17 mb/sec. I copied 30gb file and reached this speed. During this proccess, my laptop was really slow. When I open a new tab and trying to write something or view the web-site was kinda slow. Or openning a file took more than normal and It was annoying. I was a vista user and I don't know what they changed for Win 7 because I didn't use it. Now I'm a Win 8 user and find this weird. Vista was installed on my old laptop and if I run into these things, I'd say Ok but I guess I shouldn't face this problem with these specs. Do I have a problem or is this Win 8's nature?

The specs are:
Toshiba 1 TB 5400 RPM 8MB cache