The “ultrabay” is an optional component that can be plugged into the Lenovo Y500 and provides another GT 650M GPU. The GT 650M SLI offers a more than a GTX 670MX gaming power in most cases (see review). It is plugged in place of the DVD. You have to use latest Nvidia Drivers and the “Nvidia Geforce experience” software. You’ll also need the Ideapad 170W PSU to activate the GT 650M SLI, according to Lenovo.
For this price, it is an excellent addition to those of you who want the additional power.