Over the years, the computer industry has seen a wide number of different video connectors. The VGA standard helped bring high resolution and color displays away from the first TV video connectors. DVI introduced us to digital displays that allowed for greater color and clarity. Finally, the HDMI interface integrated a digital video and audio signal into a single cable for use with home theater and even PC displays. So, with all of these advancements why is the industry now producing the new DisplayPort interface? That's precisely what this article looks to explain.
Limitations of Existing Video Connectors
Each of the three major video connectors has problems that limit their use with future computer display. Even though they have addressed some of the issues, some still remain. Let's take a look at each of the formats and the problems that they have:
VGA or DSUB-15
- Variable resolution/color support depending upon video card/display DAC's
- Analog signal reduces color and clarity of signal
- Heavy cabling requires connector be screwed into card/display
- No copy protection support
- No audio support
- Single DVI limited to 1920x1200 resolution with 24-bit color
- Dual-link DVI limited to 2560x1600 resolution with 24-bit color
- Heavy cabling requires connector to be screwed into card/display
- No audio support
- Version 1.3 supports up to 2560x1600 resolution with audio stream
- Version 1.1 supports up to 1920x1200 resolution with audio stream
- Category 1 cables limited to 5 meters in length
The biggest problem with the various connectors at this point is really the resolution. The maximum supported resolution is 2560x1600 which is currently achieved with the 30-inch LCD panels available. This isn't a problem when it comes to HDTV as it is limited to a 1080p or 1920x1200 resolution but computer displays tend to be much more detailed. Content protection is also pretty much a requirement for all high definition video support at this time.
DisplayPort was developed among the members of the Video Electronics Standards Association. This is a group of roughly 170 companies that develops and decides standards to be used with computer displays. This is not the group that developed the HDMI standards. Because of the greater demands of computers and the IT industry, the VESA group developed DisplayPort.
In terms of physical cabling, the DisplayPort cables and connectors look very similar to the USB or HDMI cables that are used today on most computers. The smaller connectors makes for easier cabling of the system and allows the connector to be placed on a wider range of products. Many thin notebook computers can't properly fit a single VGA or DVI connector currently, but DisplayPort's thin profile allow it to be put on them. Similarly, the narrow design allows up to four connectors to be placed on a single PCI bracket in a desktop PC.
The current signaling methods used on the DisplayPort connectors also allow for a larger amount of data bandwidth over the cable. This allows it to expand beyond the current 2560x1600 resolution limits of dual-link DVI and HDMI v1.3 connectors. This is not really an issue for existing displays, but it is important for the future growth of the display market to higher resolution displays. In addition to this video stream, the cabling can also support an 8-channel uncompressed audio stream similar to that of the HDMI connector.
One of the major advances with the DisplayPort system though is the auxiliary channel. This is an additional channel to the standard video lines in the cable that can carry additional video or data information for more demanding applications. An example of this can be the connection of a webcam or USB port that is built into the computer display without the need for additional cabling.
DisplayPort More Than Cabling
Another important advance with the DisplayPort standard is that it moves beyond just the connector and cable between a PC and display. The technology can also be used inside the physical displays of a monitor or notebook to reduce the amount of connectors and wiring required. This is due to the DisplayPort standards including a method for direct display connections.
What this means is that the display can remove many electronics necessary to convert the video signal from the video card into one that can be used to drive the physical LCD panel. Instead, the LCD panel uses a DisplayPort drive that bypasses this electronics. Essentially, the signal that comes from the video card directly controls the physical state of the pixels on the display. This can allow for smaller displays with fewer electronics components. This can conceivable allow prices of the displays to drop.
With these features, it is hoped that the DisplayPort can be integrated into a wider range of products other than computer displays, PCs and notebooks. Smaller consumer devices could also integrated the DisplayPort connector for use with compatible monitors.
Still Backwards Compatible
While the DisplayPort standards currently don't include any backward compatible signaling within the physical cable and connectors, the standard does call for support of the older display standards including VGA, DVI and HDMI. All of this will need to be handled through external adapters. It will be a bit more complex than the traditional DVI-to-VGA style adapter but still contained within a small cable.
While DisplayPort is still in its early stages with only a few products released in late 2007, there is a lot of potential for the video connector. The real test for it will be how it is integrated beyond computer products. HDMI is heavily entrenched into the home theater market and is making progress with PC companies. Displays are not likely to really go beyond the 2560x1600 resolution or 24-bit color depth in the near future either. The other key feature will be the auxiliary channel to be used for carrying other data beyond the video signal. This is one that many notebook manufacturers might be willing to pick up on to simplify their designs and products.