Verdict: The first monitor to use USB as a display interface.
The DVI connection is under threat. Consumer electronics have moved over to HDMI, as it's easier to plug in and it integrates audio, too. Meanwhile, the first DisplayPort graphics cards saw the light of day in December 2007, but there's another contender waiting in the wings - USB. Enter the Samsung SyncMaster 940UX, our first look at a monitor that you can hook up via USB, as well as VGA and DVI, using a technology called DisplayLink.
Before we go any further, however, we should point out that USB 2 will never be a direct replacement for DVI, as it isn't fast enough. Single-link DVI-D has a maximum throughput of 3.7Gb/sec, and dual-link DVI-D has double that amount, while USB 2 can muster only 480Mb/sec. This is more than enough for an external hard disk or a webcam, but it will severely limit the refresh rate available for high-resolution video. Therefore, DisplayLink screens are best used with fairly static screen content, such as retail displays or everyday office applications.
The 940UX has a fairly standard specification for a 19in TFT. It uses a TN panel, a cheap panel technology that isn't exactly renowned for its dynamic range. The native resolution is 1,280 x 1,024, with a 300cd/m2 brightness and 1,000:1 contrast ratio (or 2,000:1 if you use the dynamic contrast setting), which is all pretty much par for the course in a 19in TFT. The ports on offer are relatively standard too, with DVI-D and D-SUB, but no analogue video. However, the panel can be rotated into portrait mode, which could be handy for multi-monitor display banks.
The USB 2 upstream port is married to a pair of downstream ports, and this is where the fun starts. Hook up the screen over USB and the monitor will be detected as a DisplayLink device, with drivers installed automatically. After a reboot, your desktop will be extended to the USB screen, just as it would had you used two standard display outputs. You can then use the downstream USB-only ports to hook up devices such as memory keys as normal but, more importantly, up to three more 940UX TFTs can be daisy-chained over these USB outputs. You can even run two TFTs from one 940UX for a maximum of six screens in total.
The extra displays can be extensions of your desktop, or clones. However, under Vista, only the clone mode is available, which makes DisplayLink near pointless for Vista users.
As we explained, the bandwidth of USB 2 limits what you can do with monitors connected in this way. The TFT driver sidesteps your graphics card entirely, so there's no support for Direct3D. As the screen spanning is carried out using software, it will tax your CPU - moving a window on a DisplayLink screen pushed CPU usage up to 25 per cent on our test system's 3.6GHz Pentium 4 660, while video playback used 40-45 per cent of the available processing power. Video playback is possible via CyberLink PowerDVD, InterVideo WinDVD or VLC.
Although the 940UX's headline act is its USB connectivity, we also put the monitor through its paces with our usual suite of quality assessments when attached via DVI, and also when hooked up using USB. We started with the industry-standard calibration and setup tool, DisplayMate, and then moved on to games and video.
The 940UX was well configured when it arrived, and didn't need much adjustment. However, viewing angles weren't great - particularly vertically, as is normal for TN panels. The screen also struggled to discern dark greys from black, although it was better at the whiter end of the scale. Contrast is therefore disappointing, but images are reasonably vibrant. Our 'Lord of the Rings: Return of the King' DVD test was pleasing, even if the colour was a little muted. However, the 5:4 aspect ratio isn't great for widescreen movie viewing, and the DVI-D link isn't HDCP-compatible either. Disappointingly, DVD playback also only works in clone display mode.
The poor contrast at the dark end of the scale was revealed in our gaming tests. It was nearly impossible to see anything in the darker sections of Prey, although the gaudily lit exteriors of Need for Speed: Carbon were more acceptably displayed.
Connected via USB, the synthetic DisplayMate tests gave identical results to those with DVI-D. The game tests didn't work, but we could run our film tests. The visuals remained the same, but the frame rate became jerky as our Pentium 4 660 struggled to process the video for display. The image was also reduced in resolution (we saw jagged edges to diagonal lines, as you'd see with aliasing in a game) to circumvent USB's low bandwidth.
Conclusion
Priced at £200, yet offering only average performance, the SyncMaster 940UX seems expensive - you can now buy 24in panels for less than £300. The reason for the price is clearly the DisplayLink technology, but with dodgy performance in video playback and no Direct3D support, DisplayLink isn't ideal for anything but basic desktop use. It might be useful for a video wall, but under Vista, you'll only be able to clone your desktop across the screens rather than extend it. With DisplayLink only slightly more underwhelming than the quality of the screen, the 940UX isn't worth considering unless you have a very specific use in mind.
