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Two Headed Penguins?
dmendesf asks: "The
Octane2 workstation from SGI has a neat trick called PowerDuo
that enables a single station to be driven by 2 keyboards, 2
mice and 2 monitors. Is it possible to do the same with Linux and
USB mice, keyboards plus Dual Head videoboards?" How difficult
would it be to develop an X11 solution to do this? Now take this
a step further: could this be done with the secondary machine
a network connection away?
While I've not tried it, I don't see any reason that a PC with PS/2 mouse and keyboard, two VGA cards, and a USB mouse and keyboard, couldn't be configured to do exactly the same; run 2 X servers, one configured for the first video card and PS/2 mouse, keyboard, the second for the second video card and USB mouse and keyboard. (you may be able to use several USB mice and keyboards, in order to get as many heads as you can fit video cards in for). As ever, the pig is setting it up.
Of course, you'd need a second sound card for seperate audio, but again that's not too hard.
As for the suggestion that you could do that with X11, well, I laughed when I read that. That's exactly what X and XDMCP is designed for! Have you never heard of X terminals (not xterms)?
When X was developed, the idea was to have lots of thin X terminals and then one big beefy UNIX box to run the applications. Then windows and PCs came along, and they didn't run apps over the network (or at least not until recently).
When I was at college, I had my PC running Linux as a single head, and an NCD X terminal which I'd scrounged from my brother in my room, and in the college's computer room they had some old HP workstation being used as an X terminal. I could easily have 3 people running web browsers, e-mail and news through the one PC (+2 dumb X terminals)
Both of these X terminals were cut-down custom made machines which booted over the network, ran an X server, and broadcasted XDM/CP for any hosts that wanted to offer them a session. It presents a list of machines running XDM, and you simply double click on one, and you get a login screen. Main problem is that both of these "thin terminals" were crap - fixed resolution (at 1280x1024, so usable), but only 8 bit colour depth. Of course, a PC with no hard drive and a decent graphics card would make a better X terminal. NCD still make them - here's a more modern and useful X terminal
The problem is though, that bandwidth over the network is very much less than you get on a PCI or AGP bus - not enough for comfortably doing very graphics intensive stuff with.(back then, I was using 10Mbit, but there are still problems at 100Mbit). Fine for checking e-mail, reading news, even web browsing, but 2D graphics was painful. 3D graphics would be as well - remember that to use things like the renderer extension, (i.e. any fancy 3D GL stuff, or alpha-blending), requires the application to run on the same host as the video card is in, as the app talks directly to the video card; X is only used for the windowing bit, and for drawing basic stuff like text and buttons.
Really, to do this properly requires compressing the X traffic, like lbx or (plug) Tarantella, otherwise it's unusable.