Gefen DVI DL: Dual Link DVI + USB KVM

DVI-DL Operation and Issues

One of the most popular uses for the Gefen DVI DL is to switch between a Mac and a PC, hooked up to an Apple 30" Cinema Display, and that is the very configuration that we're looking to test today.

Connected as system 1 was the Powermac G5, with an ATI Radeon 9600 Pro Mac & PC Edition, and system 2 was a PC with a NVIDIA GeForce 7800 GTX. The 9600 Pro Mac & PC Edition has one dual link DVI port, and thus, has no problem driving the 30" display, as does the GeForce 7800 GTX in the PC.

Now, the 30" Cinema Display has its own 2-port USB hub built into the back of the unit, and that was the hub that we had plugged into the Gefen unit. The keyboard and mouse were plugged into the Cinema Display's 2 ports. The problem with this arrangement was that when switching back and forth between Windows XP and OS X, the USB interface would always drop out when switching back to the Mac. The USB devices that we had hooked up to the DVI DL were an Apple USB keyboard and a Logitech MX1000 mouse, so whenever we'd switch back to the Mac, there would be no keyboard or mouse support. By plugging the keyboard and mouse directly into the two ports on the DVI DL, we averted the problem (we later fixed the problem through another method).

By default, the DVI DL does have some stipulations that you have to work with in order to actually get the switcher to work. First and foremost, you cannot switch to any machine that you haven't booted while switched to. For example, with both the Mac and PC connected to the switch box, I started the G5 up and I was switched to it. If I had turned the PC on while still being switched to the G5, I would not get any display on the PC. In order to turn the PC on, I would have to switch over to the PC, then turn the machine on and wait for it to boot.

With both machines up and running, it was time to give the DVI DL a try. Starting on System 1 (the Mac), we hit the Select button and switched over to System 2 (the PC). Ta-da, it worked. Now, time to switch back, but unfortunately, switching back wasn't as smooth of a process.

The screen had artifacts all over it and the mouse cursor had turned into one giant block.

That big block? That was our mouse cursor.

We traced the problem down to Safari, and to be more specific, any visible Safari window with any animated Flash on it. If we hid Safari before switching to the PC, or left it on a page with no animated Flash, then there was no corruption. But if we didn't do one or the other, then we usually came back to a screen full of artifacts and a nice big block to act as our mouse cursor.

We contacted Gefen, which offered extremely quick turn-around on all tech-support queries (generally, all questions were answered within 24 hours on their forums). Gefen insisted that if we wanted a solution to the problem, we would have to purchase a DVI Detective. Gefen's DVI Detective is a programmable device that records your monitor's EDID information and constantly transmits it to the computer to which it is connected, so regardless of whether or not the monitor is actually connected to it, the computer thinks that it is.

Given the price of the DVI DL switcher, the functionality of the DVI Detective should honestly be built into the device, but for whatever reason, it isn't. Granted, this isn't exactly Gefen's fault, but rather a problem with the way that OS X in combination with the ATI Radeon 9600 Pro handle a disconnected DVI signal, as the PC worked just fine. But given that a number of 30" Cinema Display owners may be turning to the DVI DL, it is an issue that is worth noting.