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The Peculiarly Quiet Decline and Fall of the KVM

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21–30 of 145 posts

Re: The Peculiarly Quiet Decline and Fall of the KVM

#21
Wendell, from the YouTube channel Level1techs, has worked with a Chinese(?) OEM on custom firmware for Displayport KVMs and is selling them:

https://twitter.com/tekwendell/status/933441036138971137?s=1...

Still more expensive than a 4k monitor, but heading in the right direction.

Re: The Peculiarly Quiet Decline and Fall of the KVM

#22
Ironically, to me personally KVM [1] is reason #1 for not owning and using the other KVM [2]. I simply do not need an additional physical machine as what I need is available in a VM at no cost with plenty of performance.

[1] https://en.wikipedia.org/wiki/Kernel-based_Virtual_Machine

[2] https://en.wikipedia.org/wiki/KVM_switch

Re: The Peculiarly Quiet Decline and Fall of the KVM

#24
post #3

PSA: It's about this "KVM": https://en.wikipedia.org/wiki/KVM_switch Not this: https://en.wikipedia.org/wiki/Kernel-based_Virtual_Machine

I opened the link because I was wondering what is it talking about when KVM (the virtual machine) is more popular today than ever. :)

Great, so there won't be confusion anymore! :)

Re: The Peculiarly Quiet Decline and Fall of the KVM

#25
KVM switches used to be a huge and super important (and expensive) thing in rack server farms back when every rack or every few racks had a pull-out tray with a keyboard and a monitor. Technology moved on. First the tray and monitor disappeared with KVM-over-IP, which saved many trips to the server room. Then the KVM switches themselves disappeared, as manufacturers integrated out-of-band remote access into the servers, first with add-on boards, then onboard and finally on-chip (this is what Intel AMT does, when it isn't busy running rootkits).

The little two-PC switch box the article refers to (I think) was always a spillover from the server KVM technology, except with a very small market and more difficult to make. Servers don't need sound and are fine with just VGA video. Home computers want USB (which variety?) and audio switched, or high bandwidth signals that are very touchy about interference or suddenly being connected to a different device like HDMI, Displayport or Thunderbolt. And then people want the stuff for cheap.

> signal switches with arbitrary bandwidth remain available: analogue relays

Have you tried that? Cut a HDMI cable in half and splay it out, then try switching that to another display. See what happens. If it were that easy, it'd be around (or you'd just be building it yourself).

Re: The Peculiarly Quiet Decline and Fall of the KVM

#26
post #15
post #9

The main thing that has pissed me off with technologies like DisplayPort and HDMI is that I cannot actually turn my monitors off when I'm not using my computer. With DVI I could turn the monitors off and the desktop and applications would stay where they were. With HDMI/Displayport it considers the monitor disconnected, hence re-adjusts the desktop and moves everything around. I would love an option that I could swit…

You must have some dodgy hardware. This is definitely not normal, at least with HDMI. I just tried it with the monitor right in front of me, even unplugging it from the wall didn't cause the laptop to drop the monitor like it would if I had disconnected the HDMI cable.

What I had learnt from investigating this issue is:

* It's been a problem since at least 2012

* HDMI cables have an active-low connection pin, therefore it's easier to fool the video card into thinking the monitor is still connected.

* DisplayPort is an active-high signal, therefore if the monitor powers off, it's the same thing as the cable being physically disconnected.

Ideally I would be able to switch the monitor off in such a way that it still maintains a connection, just that the display is off.

Edit: formatting

Re: The Peculiarly Quiet Decline and Fall of the KVM

#27
post #3

PSA: It's about this "KVM": https://en.wikipedia.org/wiki/KVM_switch Not this: https://en.wikipedia.org/wiki/Kernel-based_Virtual_Machine

... which makes this a total non-story in my opinion :)

Of course KVM switches will eventually disappear; when was the last time any of us (minus datacenter staff) has been to the server room since the dawn of the PaaS age?

Re: The Peculiarly Quiet Decline and Fall of the KVM

#28
The ones that used VGA ports for video often used to degrade the image quality in comparison to a direct connection.

Frankly there are entire categories of desktop computer peripherals that get a deserved reputation for being flakey junk. USB hubs used to be this way, but presumably they've finally got those right. Inkjet printers too.

Re: The Peculiarly Quiet Decline and Fall of the KVM

#29
post #6

I'd guess the comment about HDCP is onto something. To build a KVM switch that works with modern displays without weird errors, it probably has to be an active HDMI/HDCP endpoint on its own - which means a vendor would either need to get its own sets of keys and do additional work to enforce all DRM restrictions - or they'd have to use leaked keys and prepare to get sued in an instant. Even without HDCP, I remember a…

You'd need the HDCP master key, but you need not be a full-featured endpoint. See https://www.bunniestudios.com/blog/?p=2117 for an example of a device that mixes an incoming HDMI video with a (non-HDMI) overlay video. The device is sold in the US, so it must be considered legal.

Re: The Peculiarly Quiet Decline and Fall of the KVM

#30
With VGA, it was simple: duplicate the EDID to both inputs, switch the output wires, done. AFAIK, with DisplayPort it's not so simple, since there is a negotiation between the computer and the display, including link training (see https://lwn.net/Articles/736011/ for instance). IIRC, HDMI also has some bidirectional communication. To work well, a KVM would have to act as a display to the computers, and as a computer to the display, instead of just passively switching some wires.
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