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KVM switches for VGA displays vs for DVI displays: From examining prices both these days and a couple of times over the past year or two, I've noticed that, generally, 2-machine KVM switches, with USB ports for keyboard and mouse, are about an order-of-magnitude, 10x or so, more expensive for DVI displays.

DVI is newer and more complex technology, so maybe the hardware for it is a bit more expensive, but were talking about a passive component which doesn't do any DAC, just switches wires. So where does the 10x price difference come from?

I realize that DVI-based KVMs are newer on the market. However, DVI has been around for more than a decade already; and while VGA KVMs have been around for longer, they used to have PS/2 connectors rather than USB ones. So the age difference doesn't explain such a price gap. Also, I'm not comparing apples and oranges w.r.t. audio connector switching, or massive metal vs lightweight plastic boxes.

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Your assumption that the KVM is a passive component is wrong. Even with VGA, the KVM has to correctly manage access to the EDID in the monitor. The video sources cannot read the monitor EDID simultaneously. However the video signals are totally analog so once the sources know what format to send, they can be switched in and out as needed.

DVI (the digital part) is not just unidirectional signals, there is a whole protocol that requires timing synchronisation on both sides of a link. On top of that is HDCP where encryption keys need to be synchronised.

There might be some clever trickery to reset the links every time the video source is switched, but I think the normal way to do this is to decode the video data in the KVM, then re-encode for the monitor. This means the links to the monitor and video sources needn't be reset all the time. However, to do this you need a rather powerful FPGA (or bespoke ASIC) to at least maintain multiple input links and to forward the right video data to the output links.

In addition to all that, I'm sure there's a lot of testing to iron out quirks in different devices. These are probably widely known for VGA, but not so much for DVI.

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    If a homunculus pulled the video cable out of my video card causing my multi-monitor setup to be upset, I'd pull the homunculus out of the KVM switch and stab it repeatedly. – Ignacio Vazquez-Abrams Jul 28 '18 at 21:48
  • don't forget that DVI KVMs need to support both VGA(DVI-A) and HDMI(DVI-D), for this reason HDMI KVMs are less expensive than DVI – Jasen Jul 28 '18 at 23:12
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    @Jasen: That point could be developed into an answer. – einpoklum Jul 28 '18 at 23:16
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    @sawdust: The desk I am sitting at right now has two monitors and two computers. One monitor is exclusively connected to my workstation via HDMI, and the other is connected to my workstation via DVI and the other computer via VGA. If I were to use a DVI KVM switch for the second monitor then my workstation would detect any disconnection and switch my desktop to a single monitor. And don't get me started about when I tried using a HDMI switch on my primary monitor; that was an exercise in pain... – Ignacio Vazquez-Abrams Jul 29 '18 at 1:52
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    @sawdust : not so confusing. The KVM may well have some ports marked as "input" (e.g., data coming from a computer) & different ports marked as "output" (e.g., data going to a monitor), for the sake of user-friendliness, even though you're technically correct that one of the devices plugged into an "input" port may actually be performing "output" during bi-directional communication that a protocol requires. As another example, although a monitor can send info to a PC (so the PC can determine whether something is plugged in), monitors are still typically classified as output devices (not I/O) – TOOGAM Aug 3 '18 at 13:43

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