USB video?

Ben Scott dragonhawk at gmail.com
Sat Feb 15 19:51:00 EST 2014


On Tue, Feb 4, 2014 at 1:17 PM, Tom Buskey <tom at buskey.name> wrote:
> Why do servers still have VGA + PS/2?

  From what I see, most have VGA and USB, these days.

>  Because most KVMs haven't switched?

  I'm not privy to their design meetings, but I would suppose:

  VGA is cheaper, both to build a video source, and to build a switch.
 DVI has higher connector costs, cable costs, and tighter signal
tolerances than VGA (especially at lower resolutions).  VGA only needs
5 conductors for a minimal implementation.  DVI may also have
mandatory and/or more complicated metadata signalling (vs VGA); that I
don't know about.  Plus, as you note, KVMs already had them; changing
creates a compatibility headache to no gain.

  USB vs PS/2: USB connector is flatter (important in pizza box form
factors), and cheaper, and more rugged.  USB is hot-swappable, which
means it's cheaper to build a switch -- you don't need to proxy the
mouse, the way you do with PS/2.  And you only need one channel from
the switch to the computer(s), since the protocol supports
multiplexing (hubs).

> FWIW, I still have a KVM that will do serial mice.

  I used to, too, but it was bigger than most of the servers it would
have been hooked up to.  ;-)

-- Ben


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