KVM H3LL link page          

Keyboard Video Mouse, KVM (or  you can call it a human interface MUX  , or HID human interface device that has a multiplex switch inside)
This painful device allows you to use 1 set of KVM devices, on many PCs shared.
The big problem is the stinking VESA evolutions of controls for 2 decades.  (eDID is newest is best)
The end of PS2 devices, mutating to USB keyboard and mouse (wireless forget that, mostly) (makes old PS2 KVM , boat anchors)
The Video choices now are many, VGA, DVI, HDMI , DP and mini DP. (no KVM can do all those, maybe 1) {and using adapters,  you will fail}
If the monitor is old or the KVM is old new PCs will not understand that the DDC pins moved. (VESA changed many times)
The whole KVM idea today is wacky tech.  USE FREE ANYDESK(tm) and stop using KVM for gosh sakes.
To run headless , lick the above link.  (headless means no monitor or mouse or keyboard at all any where neat those PC's)

Yes a modern KVM works on any modern PC. (mostly)
The other show stopper is when you switch live KVM from PC1 to 2 or what ever, if the PCs GPU  card does not support hot swap eDID feature the next PC is born dead.
The KVM can do this 2 ways, it just lies to the PC (target) and tells it resolution is.1080p and most times this works, or the KVM just is pass-through devices and simply gates the MONITOR you have, eDID data to the PC.
If the monitor you have is hot swap eDID certified this fails.
The hot swap is the GPU card first sends 5vdc power to one of the port pins, and the eDID chip in the KVM must wake up and send the plug and play data seen in the link above, if not the PC switch you did fails. hard.
KVM switches over via 1 of 2 ways or both; a button, or just hot key on the Keyboard.  (control +K)? no 2 KVM work the same way, RTM.

There is nothing simple about KVM switches, unless lucky like the Irish.
The worst are using older KVM, and for sure old USB Keyboards ,mice or KVM  from 1995.
Windows 10 HOME , the worst of the worst. (get Pro)

Enterprise, servers, are whole other matter. My Dell use DRAC. (R710  I have) I can even turn the server on from 12,000 miles away, with DRAC.
KVM over, IP, or like HP , iLo remote access via its own IP subnet, (using generic, Ethernet switches) (or use Anydesk ,like me)
This 1st photo below is pure hell, it works on only the old system (any makers brand)  as you now see, KVMs are sometimes huge. (and very LEGACY)
If you never turn off the PC or server, ANYDESK(tm) is your answer, and FREE for home use.

And more lost more , and endless stream if KVM , for 2 decades of PC and Servers.

version 2.  8-4-2018