One company that many of our readers are likely unfamiliar with is DisplayLink. We received a press release from them prior to CES and decided to stop by and see a demonstration of their products. The concept is pretty simple, and it's not something everyone will benefit from, but if you've ever wanted to add a second display without worrying about upgrading video cards you'll appreciate what they've created. DisplayLink provides technology that allows you to hook up additional displays via a standard USB connection. DisplayLink also has partners like Samsung where the technology is integrated directly into a display - a 19" LCD was released in June with this functionality and more offerings are planned.

If you're quick at math, you're probably already wondering how they manage to deal with the limited bandwidth. DisplayLink says that they're currently doing well with around 200Mbit of throughput, though they are able to scale down quality if necessary. What they have is a software display driver, and they only transmit actual updates over the connection. Ideally, everything is done with lossless quality, but the technology is intelligent enough to deal with reduced bandwidth. Lossy compression comes next, followed by a reduction in color depth, and finally frames are dropped if necessary.

They demonstrated systems running anywhere from one to many additional displays, with static images, animated desktops (running a script), and streaming video content. Depending on the intensity of the content being shown, the experience ranged from very smooth to slightly choppy at times, but for desktop usage patterns we definitely didn't see anything unacceptable. Video streaming even worked reasonably well at moderate resolutions, with full screen 1680x1050 showing some definite loss in quality.

Besides wired USB connections, DisplayLink works with other companies to provide wireless display connectivity. DisplayLink uses WiMedia as the physical UWB (Ultra Wide-Band) communications layer, and on top of that they run the Wireless USB protocol. This isn't something where you'll be able to transmit your display content throughout a large house, but they are working at providing wireless display support within the same room (approximately 15 feet). Throughput within the same room is getting around 120Mbit with the potential for up to 200Mbit. Theoretically, 480Mbit (Wireless USB) is possible, but just like regular USB and WiFi you can't actually get the full bandwidth. Note that WiMedia's maximum bandwidth is #ff0000, but most likely they won't get more than 300Mbit in ideal circumstances. They told us that 802.11x WiFi support didn't work out well due to inconsistencies in throughput - it's not uncommon to get 100Mbit one moment and 30Mbit the next with 802.11n, for example, so they turned to WiMedia and found that the bandwidth consistency was much better.

Resolution support is currently somewhat limited, though more than sufficient for most users. They currently support 1600x1200 maximum (or 1280x1024 on a lower end chip). They are working at providing 1920x1200 with a new chip, which is due to be released later this year. While it's still in beta status, they did provide a live demonstration of 1920x1200 output. Another upcoming development they demonstrated is that Intel has been extremely impressed with their work so far, and since Intel doesn't have any discrete graphics market to protect they worked with DisplayLink to integrate the necessary code directly into some test GMA X3000 drivers. With the improved performance brought about by this change, they were able to demonstrate 720p content with little if any loss in quality.

For our greedy readers (Ed: you know who you are!), you're probably wondering how far you can push this technology in terms of display count. As an example of the extreme end of the spectrum, they had a demonstration of a laptop running six displays (via a single connection to a USB hub). There was definitely a bottleneck in terms of bandwidth in this configuration, but if you aren't planning on streaming video to multiple displays you could easily have multiple monitors all displaying different content. Remember: as long as nothing changes on the display in question, no bandwidth is used. So if you wanted to have a second (or third or fourth…) LCD showing a static document while you work on the main display, this would be a perfect solution. This particular configuration was consuming about 100MB of memory for the DisplayLink software, ~33% of the CPU time (on a Core 2 Duo T7100), while Windows Media Player used another 15-20% to play a video on one of the displays.

Let's get a few other things out of the way now by explaining what DisplayLink does not do very well. For one, gaming support that requires a discrete GPU is basically out of the question. The DisplayLink adapter is a virtual display device with its own resources. It works well enough in Windows - XP and Vista are supported - but certain content obviously has more difficulty running well. Video streaming was demonstrated and it worked well enough, but in full-screen mode at 1680x1050 you can definitely see some choppiness and compression artifacts. We tried to get a demonstration of doing two simultaneous video streams (on Windows Vista - XP only supports overlay mode on one screen at a time, so it's not possible there), but we were unable to do so in the time we had at their suite. However, we do have some hardware to test, so we will look at other options in the near future. DisplayLink also has a version of their software scheduled to come out for OS X in the next few months.

The primary target market appears to be businesses, particularly those looking to improve productivity by adding a second display. However, there are certainly many others that would be interested in using this sort of technology. We will try to get additional information on pricing and availability for the various products.



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  • strikeback03 - Wednesday, January 9, 2008 - link

    VLC player has an option to not use overlay for video output, so I'd guess you could try this for multi-display in XP. Reply
  • Lonyo - Wednesday, January 9, 2008 - link

    Well I know that I have run 3 h264 encoded videos through MPC (Media Player Classic) on 3 monitors simultaneously (2 connected via 1 graphics card, 1 connected by a second card), with output set to "system default", under Windows XP, so it's easily possible. Reply

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