The Decklink Quad 3G-SDI Mezzanine Card for Decklink 4K Extreme 12G from Blackmagic Design is a replacement for the original daughter card that came with your Decklink 4K Extreme 12G PCIe board. The daughter card features four BNC connectors that support 3G-SDI. The four connectors are grouped into two input and two output connectors that work in conjunction with the four 12G-SDI connectors on the main board. Replacing your original daughter (mezzanine) card with this one expands your cards input and output capabilities. Replacing the original HDMI/optical fiber output daughter card with the Quad 3G-SDI board allows you to input and output a Quad 3G-SDI signal, which the main board cannot do by itself. Another input/output capability of the card is to input a 12G-SDI signal and output a Quad 3G-SDI signal. Requires 10.4.2 driver to operate. This daughter card only works when connected to the optional main board.