| Dual-Link DVI
IntroductionWith the advent of extremely high resolution displays (such as the 30" offerings from Apple and Dell), conventional single-link DVI connections are not able to keep up. To remedy this problem, newer graphics cards are begining to offer dual-link outputs to drive these monitors. The nVidia 7000-series and ATI x1000-series cards all offer at least one dual-link output, with the higher-end cards offering two.
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Single-Link DVIThe DVI standard defines a total of six high speed data lines that can be used to deliver images to the connected monitor. Most monitors, however, only use three of these lines (one for red, one for green and one for blue) in order to save costs. These devices, in turn, are called single-link DVI devices as the second set of data lines are left unused.
A single-link DVI connection is theoretically limited to a maximum resolution of 1600x1200@60Hz (approximately 115 million pixels per second). By adjusting some parameters (see below), it is possible to push this limit up to 1920x1200@60Hz (~138 million pixels per second). In order to reach resolutions above these, it is necessary to make use of the second 'link' provided by the DVI cable.
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Vertical Blanking IntervalConventional CRT monitors draw images by scanning the picture tube from the top left corner and work their way to the bottom right. As such, at the end of each frame the video signal must temporarilly pause to give the monitor time to move the beam back to the top left corner. Like it's predecessors, the DVI standard provides this vertical blanking interval in order to support these monitors.
When using a LCD, however, this blanking interval is not necessary as the underlying technology is very different. As such, the time spent on this blanking interval can be used to send additional image data. This allows video cards to push the single link resolution limit up to 1920x1200 rather than the theoretical 1600x1200 limit. Nearly all modern graphics cards support this functionality so dual-link is not necessary to drive the LCD monitors that reach these resolutions.
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RequirementsAs dual-link DVI connections double the bandwidth, monitors making use of this functionality can reach resolutions as high as 2560x1600@60Hz. As such, the new crop of high-resolution 30" monitors require video cards that can deliver the video signal via all six wires in the DVI cable. These dual-link DVI connections do not physically look any different than single-link ones, so it is important for users of these monitors to pay close attention to the specifications of the video cards they are buying.
It is important to note that a dual-link graphics card will function with a single-link monitor without any trouble. If the monitor does not make use of the second set of data lines, the video card will simply revert to single-link mode. The second link is only activated when a dual-link monitor is attached to a dual-link video card. As such, even if users don't need dual-link capability at this stage it is often a good idea to keep it in mind for future expandability.
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AvailabilityWhile dual-link capability was relatively scarce not too long ago, most of the current offerings on the market now offer at least one dual-link DVI connection. Unfortunately, users with older generation graphics cards may need to upgrade to get this capacity.
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Video CardsThe following table shows a number of currently available graphics card families and the number of dual-link ports provided by them. This is not a complete list, however it covers many of the more popular offerings that are on the market right now.
| Manufacturer | Chipset Series | Dual-Link DVI Ports |
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| ATI | Radeon X1900 | 2 |
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| ATI | Radeon X1800 | 2 |
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| ATI | Radeon X1600 | 1 |
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| ATI | Radeon X1300 | 1 |
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| nVidia | GeForce 7950 | 2 |
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| nVidia | GeForce 7900 | 2 |
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| nVidia | GeForce 7800 | 2 |
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| nVidia | GeForce 7600 | 1 |
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| nVidia | GeForce 7300 | 1 |
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| nVidia | GeForce 6-series | No |
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Note that the capabilities listed here are based on the underlying GPU - the OEMs making cards based on these chips may or not implement their full functionality. Users should check the specifications for the individual cards they are looking for.
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MonitorsThere are only a small number of dual-link capable monitors currently available to mainstream markets. While there are a number of devices being offered for specific medical and technical markets, they are generally not suitable for image editing tasks so they are not mentioned here. - 30" Apple Cinema Display - Apple's flagship monitor, offers a 30" 2560x1600 LCD panel with an alluminium chassis and built-in USB and Firewire hubs. Does not support HDCP capabilities.
- Dell UltraSharp 3007WFP - Dell's 30" 2560x1600 LCD panel in a polycarbonate chassis with a built-in 9-in-2 card reader and USB hub. Provides full support for HDCP encryption.
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See Also- DVI - General article on topics surounding the DVI standard and it's uses.
- VGA - Article on the analogue video standard used by many conventional monitors.
- HDCP - An encryption standard used to allow the playback of rights-managed high definition content on computer monitors.
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External Links
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