Sithex,
High to medium end Intel and AMD CPU's have an integrated graphics processor (IGP) on the CPU die these days. This means that there is a tiny graphics card on your CPU, apart from the 750 ti graphics card that you already have. When you play games, your computer automatically decides which graphics card to use, based on (1) where you plugged the screen into (750 ti or rear motherboard HDMI port next to audio jacks), and (2) if the primary video adapter in BIOS was selected as onboard graphics (IGP) or the add-in card (750 Ti).
Given the CPU that you've specified (i5 4460), it is safe to say that you have an Intel® HD Graphics 4600 IGP on your CPU. Ref...