These two are different types of digital formats available for DVI connection. There are many different formats within the DVI standard. These include Single-Link and Dual-Link DVI-D formats, as well as Single-Link and Dual-Link DVI-I formats. All DVI cables send information using the TMDS protocol. In the case of single-link DVI cables, they use only one TMDS 165Mhz transmitter. In the case of dual-link cables, this is two. The dual connection DVI pins effectively double the transmission speed and improve the efficiency of the signal.