How Do KVM Switches Work?

The KVM Switch traditionally takes input from a keyboard and mouse and routes it to one of two computers. The switches are not merely mechanical so it's not a matter of getting some fancy Y-adapters and making your own. At the same time the keyboard and mouse are switched, resulting input from the selected computer is routed through to the video output to the master monitor.

While this may seem confusing, the diagram at the right should serve to show the typical connections of a KVM switch. The challenge when providing a PC/Mac KVM switch is that the majority of switches utilize standard PS/2 connectors for keyboard and mouse. Macintosh computers (at least since the G3) take USB only. In addition, many KVM switches utilize VGA output for the video 舑 which is adequate, but downgrades some of the quality inherent in many new digital displays. Enter Gefen and the USB Switcher. Employing a USB switcher with DVI video, they provide an up-to-date solution for connecting two computers, or any flavor up to a single keyboard, mouse and display device.

Setting Up the USB KVM Switcher

Let me make this perfectly clear. Gefen provides absolutely everything one would need to successfully connect two computers via the USB Switcher. No matter if you plan to use analogue or digital monitors, you have the necessary adapters and complete cabling you need to mate two computers within a 6' proximity to each other.

I opened up the USB Switcher and was rather surprised to find a few additional items along with the main device:

• Two 6ft DVI-A to VGA Cable
• One DVI-A to VGA Adapter
• Two 6ft A to B USB Cable
• Two 6ft Audio Cables

Why was I surprised? Because many companies provide a solution without taking into account the way a majority of people will use the device. The presence of the DVI-A to VGA cables allowed me to utilize the VGA outputs on my ATI Radeon 9700Pro display card (PC) and ATI Rage Pro card (Mac). The included DVI-A to VGA adapter allowed me to send the switched output to my "low-tech" non DVI-enabled 17" Dell monitor. The included 1/8" stereo mini audio cables were a nice touch and allowed me to route the audio output from both computers to the USB Switcher and then continue the output to my office audio system (a Pair of B&W 601s with a Velodyne SPL-800 subwoofer - all driven by a Yamaha stereo receiver.)

Performance and Switching

Switching is surprisingly instantaneous and flawless. A single pushbutton on the front of the USB Switcher controls the switching process from (in my case) Mac to PC. A green LED is present which indicates whether CPU 1 or CPU 2 is connected to the input and output devices. Both computers were able to successfully wake up from sleep modes and work immediately after switching the box from one to the other. The WindowsXP PC (an Athlon 2500+ system with nForce2 chipset) would give me the telltale USB hardware found "dong-ding" tone each time I switched back from the Mac, however it never once reloaded drivers or delayed usability unless it occurred between the time my finger left the switch button and touched the mouse (which I can live with!)

On an ergonomic note, I recommend placing the unit within easy reach (I placed mine atop my current PC) so that you can easily hit the select pushbutton. The Gefen KVM switch has rubber feet and does a solid job of sticking in place when I select the pushbutton - something I was initially worried about with its placement.

Neat Tidbits on Macintosh and PC Compatibility

When I first set up the USB Switch I didn't know what keyboard I would be able to use. My home built PC utilized a PS/2 keyboard - something the USB Switcher is (purposefully) not designed to operate or incorporate. My Mac G4, on the other had, utilized an Apple Pro keyboard. Surely a Mac Pro keyboard wouldn't work on a WindowsXP computer, would it? I did some research and found out that it does indeed function (and without any special drivers) with a couple minor inconveniences. The first and most annoying problem is that the 'Print Screen' functionality is missing. Pressing the 'F13' button (where the 'Print Screen' button should be) yields no response at all. In addition, the less-used Scroll Lock and Break/Pause buttons (F14 and F15 respectively) are also not mapped. The solution to this problem was found with a small program called Click-N-Type, a virtual keyboard that possesses the missing buttons - allowing me to once again capture the screen to the clipboard when needed. I simply keep this app handy and call it up when necessary.

Summary and Conclusions

The Gefen USB Switcher KVM Switch is an incredibly useful tool for anyone who has two computers in close proximity. It can save lots of time and works wonders for my job as Editor of Audioholics. Consider the fact that this box can save you the cost of an additional monitor and keyboard/mouse combo as well as allow you to be more productive by allowing more flexibility in how you work between different machines. I composed this entire review on the Mac (something I haven't done in about 2 years) and published it on the PC. The unit is built well, comes with everything the majority of users will need and is simply a well-thought-out device that brings modern technology (USB and DVI) to the world of KVM switches. The fact that they provided audio switching is simply icing on the cake and shows that Gefen took everything into account when they designed the USB Switcher. The only minor downside is going to arise if people want to use native DVI video cards with this unit. In that case you'll want to purchase a couple of straight DVI to DVI cables to facilitate non-VGA connector hookups. Given the impressive list of features and flexibility of this unit, not to mention the price tag, I can live with that.

Gefen, Inc.
Customer Service
6265 Variel Ave.
Woodland Hills , CA 91367-9897
800-545-6900
[email protected]