Controlling a mix of DVI and VGA computers using a KVM switch

Can DVI and VGA computers be controlled from one KVM switch?

Connecting computers with a mix of DVI and VGA video to one KVM switch may prove challenging. The reason: VGA video is analog, while DVI video – as the name (Digital Visual Interface) implies – is digital. Analog video and digital video are incompatible and cannot be mixed.

Additionally, the (one) monitor connected to the KVM switch uses one connection to do so.  Even if the monitor has both VGA and DVI connector-inputs, typically only one at a time can be used. If you're using the DVI (digital) connector and an analog video signal is coming in – the monitor doesn't know how to interpret it, and vise versa.

For a KVM switch to work properly when connected to computers with different video formats, all three (3) components (computers, KVM switch and monitor) must support the same type of video, either analog or digital.

Notice we are referring to 'type of video', not 'type of video connector', since 'similar' video connectors may, in fact, be very different from one another.

Enter this article's subject: How to control a mix of DVI and VGA computers via KVM switch if the video outputs are incompatible?

Here's the twist: Not all DVI connectors are created equal.

There are different types of DVI connectors:

• DVI-D – Supporting digital video only.
• DVI-A – Supporting analog video only.
• DVI-I – Supporting both digital and analog video through a single connector.

Mixing DVI-D and VGA computers
If your DVI computers have DVI-D video outputs, they are sending out only digital video signals. These digital signals are incompatible with the analog video signals coming from your VGA computers.

But why would this matter when using a KVM switch?

All a KVM switch does is accept signals coming in from computers and pass them on to a console, based on your port selection. If we can use a KVM switch (and a monitor) that recognizes and 'understands' both digital and analog video signals, then it really would not matter.

Such a switch would be a DVI KVM switch that is explicitly specified to support DVI-I (on all of its ports, including the console port), thus being able to accept and recognize any type of the video signal, digital or analog, and pass it on to the connected monitor*.

The same requirement applies to the monitor you use (connected to the switch's console port) - it must have a DVI-I connector which accepts and displays any type of video signal that comes in, digital or analog.

Of course you will also need to use VGA-DVI adapters (or adapter-cables) to connect the KVM switch to the computers with the other-type video output.

Some DVI KVM switches that are explicitly specified to support DVI-I include:

• MiniView DVI USB KVMP/KVMA
• AdderView PRO
• DVI + Audio USB KVMPs

Another option is to convert one type video signal to the other format (before connecting to a KVM switch), so that all video signals coming into the switch are either digital or analog.  Such video-format conversion gets achieved using a video converter.

For example, if you have 3 VGA computers and one DVI-D computer, you would be better off sticking with VGA - deploying one DVI-to-VGA converter along with a VGA KVM switch and VGA monitor to complete your installation.

But the need to convert a video format adds yet another device between the computer and the KVM switch, which makes installation more complex and cumbersome.  Also, video converters are not inexpensive, so naturally you would want to deploy as few of them as possible.

Mixing DVI-I and VGA computers
If your DVI computers have DVI-I video outputs, they are sending out both digital and analog video signals. The analog signals are compatible with the video signals coming from your VGA computers. In this scenario, since the common denominator video is analog, you are, in effect, using analog video across the board (from VGA computers; from DVI-I computers, and into a monitor).  As such, you might as well use a less-expensive VGA KVM switch along with a VGA monitor.

If you must use a DVI KVM switch and a DVI monitor, it is imperative in this scenario as well that both the switch and the monitor support DVI-I (thus recognizing and accepting analog video via the DVI connectors).

Once again, you will need to use VGA-DVI adapters (or adapter-cables) to connect the KVM switch to the computers with the other-type video output.

Bottom line
1) It is imperative to be able to ascertain what type DVI is supported by your computers, switch and monitor. Visually ascertaining the type of DVI may prove difficult, and sometimes may be deceiving (some manufacturers use DVI-I connectors but only support DVI-D). Consult with the technical specifications of your devise to accurately ascertain the supported type of DVI.

2) To successfully connect computers with a mix of DVI and VGA video to one KVM switch – you need to first 'level the video playing field' so that all three (3) components (computers, KVM switch and monitor) are compatible with either analog video or digital video (or both).

3) It is important to realize, however, that at "normal" resolutions – you most likely won't be able to tell a difference in quality between VGA video and DVI video, therefore you will not be compromising video quality by sticking with VGA (see "VGA vs. DVI Showdown").

* Some exceptions apply, especially with multi-screen KVM switches.

Need help? Call KVMGalore at 1-800-636-3434 or submit your question.