Its for both. You just need to buy a 2.5 to 3.5 adapter tray if you do not have a 2.5 mount in the desktop. 2.5 is standard in laptops. Many available. see below for a few.

This is laptop size hard drive. 2.5 inch. I placed in my Dell Studio XPS prior to installing in a desktop to see how it worked. And it worked well. But used in desktop to speed it up as my XPS already had a older Intel SSD. If your laptop doesn't have a SSD, you will find it speeds its boot time up tremendously just use the Samsung magician software they provide. The software will guide you through. One problem though, laptops only have one internal hookup, so to migrate your system from your present drive to the Samsung you need to make sure it will all fit or buy a larger SSD and use a USB (preferably 3.0) or ESATA adapter hook up for the new SSD drive. I did not do this so not sure how well it works, but I did see that Samsung had it on their Magician software.