You either have to: 1.) replace your current HDD with the SSD or 2.) remove the SuperDrive CD burner and replace with your current HDD and put the SSD in the original place that the HDD was in. The latter is the most popular because you can still use the SuperDrive via USB by purchasing external case for the SuperDrive and you just plug and play with the USB, therefore having a HDD and SSD. Also, with the latter, you must purchase an OptiBay expansion kit to be able to place the HDD into the SuperDrive bay.