Inside CNET Labs: DisplayLink technology uses USB to display on monitors

It is an under-reported fact, but the majority of desktop systems sold today come with only a single display port--usually VGA or DVI. If your system falls into this camp and you want your system to use multiple, simultaneous displays, you might think you are out of luck. If the folks at DisplayLink have their way, however, connecting a second display might suddenly become ridiculously easy.

DisplayLink is proselytizing a technology that allows displays to connect to computers via a regular USB 2.0 connection. While not every computer has a second video port, most have multiple USB ports (although, depending on how many peripherals you have connected, you might not necessarily have a free USB port).

DisplayLink's technology is already starting to appear in monitors, docking stations, and adapters. The Docking stations and adapters have the advantage of being potentially inexpensive and therefore allowing users to cheaply and easily repurpose older displays as secondary monitors or external displays for laptops. Some of these devices even include firmware that seamlessly download the necessary drivers to your Windows machine.

The 20-inch LG L206WU is a new LCD monitor that includes DisplayLink support. Installation was a snap on my Windows XP system, and it did not even require a dreaded system reboot. As soon as the drivers loaded from the monitor's firmware, the L206WU kicked in at the correct resolution and as an extension of the existing Windows desktop. Setting up a secondary display was never this easy.

The image-quality of the L206WU via the USB connection was comparable to that of via the traditional DVI connection. Performing typical functions such as displaying Web pages and dragging windows were smooth. Video playback, however, displayed a few chinks in DisplayLink's armor. I used the QuickTime movie trailer for Iron Man as my test clip. I started with playing back the "small" clip and worked my way up to the larger-size clips. (The clips were played back from the system's hard drive to eliminate the network connection as a possible source of latency.) The 480p clip looked fine, but the 720p clip suffered from some stuttering; while the 1080p clip was too painful to watch. Simply dragging the problem clip windows over to the primary DVI monitor resolved the playback problems. Expect to see a full review of the L206WU soon from CNET Reviews.

I also played around with a DVI-to-USB adapter prototype from DisplayLink. On one end the adapter connects to the monitor's DVI cable, and the other end connects to the computer's USB port. Installation and usage were just as simple as with the L206WU. Interestingly, the adapter faired better with the HD video than I saw with the L206WU. It wasn't until the 1080p clip that I saw any stuttering using the adapter.

On Windows XP systems, DisplayLink relies entirely on the system's CPU to drive the display to the secondary monitor. The more powerful the CPU, the less latency you are likely to see. With some Windows Vista systems, DisplayLink can utilize the existing graphics engine to help generate the display on the secondary screen, thus potentially minimizing the need to rely on the system's CPU. We didn't have the opportunity to try DisplayLink on a Vista machine, and the company claims that Vista' Aero Glass will be fully supported in a subsequent driver update.

Since DisplayLink is so dependent on software, I'm guessing that the difference in performance I saw between the L206WU and the adapter might have to do with different driver optimizations. If I'm correct, then it is possible that further optimizations can contribute towards improved performance.

Sans the HD video playback issue, I am impressed with what DisplayLink can do. I can envision at least one scenario where it could come in quite handy: when giving presentations on someone else's video projector. And depending on how powerful your system is, you can use DisplayLink technology to display on additional simultaneous displays, up to a total of six monitors.