DVI – The Digital Video Interface
The Digital Display Working Group, which was composed of the companies Intel, Fujitsu and IBM – among others – was responsible for the publication of the DVI port in 1999. The acronym DVI stands for Digital Video Interface and was the first common standard that could transfer images digitally between graphics card and display. Before this, there only was the analogue interface VGA.
Advantages of DVI
As mentioned in the previous paragraph, DVI digitally transfers images. Therefore, the process of converting images from analogue to digital, which was usual for VGA, was no longer necessary. Like this, the images can be directly and without a loss of quality transferred between graphics card and monitor.
Data transfer of DVI
For the digital data transfer DVI uses the standard TMDS. It converts the three color channels into just one serial signal that is occupied with three channels. Since the clock speed is limited to 165 MHz, the maximum resolution is 1600 x 1200 pixels. For higher resolutions up to 2560 x 1600 with 60 Hz the dual link procedure is used. By doing so, an appropriate dual link cable with more pins is used, the video data is spread on to two TMDS transmitters and the clock rate increases to 330 MHz.
Just as usual, also DVI has a maximum cable length. This depends on one hand on the damping ratio and the crosstalk of the connecting cable and on the other hand on the quality of the signal amplification. A cable length of maximum 10 meters can still provide good results, if the cable is longer than that, a DVI amplifier should be used.
Types of DVI
In contrast to VGA DVI has not only one specific pin assignment. Depending on how the pins are assigned, it can be a different type of DVI. The DVI port is divided into two parts: The analogue part on the left with up to 5 pins, and the digital part on the right with up to 24 pins. Furthermore, the DVI cables are screwable, which prevents the cable from falling out of the plug.
The different realizations of the port are shown in this picture. These are:
- DVI-A: This connector only transmits analogue signals and has 12 + 5 pins. It is usually only used as an adapter cable to VGA.
- DVI-D: DVI-D cables only transmit digital signals. They either have 18 + 1 contacts (single link) for a resolution of 1920 x 1200 pixels or 24 + 1 contacts (dual link) for a resolution of 2560 x 1600 @ 60 Hz respectively 1920 x 1080 @ 144 Hz.
- DVI-I: This transmits analogue as well as digital signals. A single link cable has 18 + 5 contacts and reaches 1920 x 1200 pixels @ 60 Hz. A dual link cable has 24 + 5 contacts and a resolution of maximum 2560 x 1600 pixels.
4K with DVI?
As already mentioned before, with DVI the maximum resolution is 2560 x 1600 pixels with 60 Hz. For higher resolutions such as 4K the successor DisplayPort has to be used.