The rear of the projector includes a cooling exhaust, a second IR receiver complementing the one next to the lens, and all of the connections other than power. You may find the connection panel rather sparse compared to older projector design that included analog video inputs. The ProBeam doesn't waste any space on those older connection types, your choice is limited to one of two HDMI inputs or an HDBaseT input for the same signals. VGA, Composite video, Component video, RGB or S-Video are generally unnecessary connections in today's environments with nearly every device today offering some form of Digital Video output. Regardless of the version found on your source – DVI, HDMI or Display Port, you can use the HDMI inputs appropriately.
However, video is not the only way to input an image on the GRU510N since it provides two USB connections with functionality to control content. There is an HID interface for mouse/keyboard operation to easily utilize the WebOS interface and content. Insert a USB drive into one of the ports and you can use the WebOS to navigate the folders and play picture or video content as well as a variety of standard file formats.
Lastly, in addition to the RJ45 for HDBaseT, there is a dedicated Ethernet port as a robust alternative to integrated Wi-Fi. Having the audio decoded at the projector often allows for a simplified system design with the projector acting as volume control and audio extractor and can greatly simplify cabling runs in some designs.