An HD SDI dual link arrangement that is configured to carry live uncompressed DCI-sized 2K footage. That is 2048×1080 pixel images at 24P, with 12-bit 4:4:4 sampling in X´Y´Z´ color space. This involves a constant data rate of at least 1913 Mb/s, too much for a single HD-SDI, designed for 1080/60I/30P 10-bit 4:2:2 bit rate of 1248 Mb/s and audio. Hence the use of a dual link.
See also: Dual link