Remote desktop sharing isn't that complicated of a concept. I use it on my Mac all the time - ssh to a server, connect VNC to localhost, you have a desktop. Is that supposed to be an enticement or a drawback? It seems straightforward to me. Apple has stuff for VNC built in, too.
Except only one user can control the computer at a time with VNC. The functionality described here means 20 students could use the same computer in theory.
>Except only one user can control the computer at a time with VNC.
Not true. You can have multiple VNC server/desktop session running on the same box, each listening on a different port, each with it's own user controlling it.
Really? I don't know much about multi-user VNC, but my understanding was that multiple users could control a machine from different ports, but they would still be sharing a single screen. That's definitely useful to know that multiple screens are possible too. I'll have to look into it more.
Don't think screens, think desktops. Each vncserver that launches (and binds to its own unique port) has its own separate desktop. Each runs its own distinct window manager application, and is not tied to a physical monitor or screen. Usually the default is TWM (minimalist window manager that takes up minimal resources), but you can also run GNOME or a host of other window managers if you want.
In OS X case, it's running the Finder.
If you log in as a user on Linux, and launch vncserver as that user, then that VNC session and desktop will be of that user.
One of the huge advantages is that the state is also maintained on the server. I've used it a LOT to install various Oracle software over the years. Fire up a VNC server session as an Oracle user, connect into it at the client site or office and start the installation. You can then disconnect, go home, do whatever, and connect in again remotely from another location (tunnelled over SSH usually), and the install will still be there running. It might have paused waiting for a dialogue to be answered, but it hasn't killed the install like logging out of the main desktop would have done.
You can also set the colour depth to be used by the client, thereby increasing performance over crappy SSH connections. 8-bit colour takes WAY less data than 32-bit, especially when installers have stupid meaningless animated gifs that run all the time.
That's the case on Windows... not sure about Mac OS. It's definitely not the case with X11 on Linux; I run multiple VNC displays all the time in addition to my normal desktop display. You can do several separate displays/desktops per user, even. The only limit is the host's resources.
As code_duck says, on MS Windows VNC just lets you see the existing single-user desktop. It's a different beast to the unix VNC.
On X Windows (X11) VNC runs 'more natively' creating a new desktop for you when you remote in - each new connection creates a new desktop instance for the user logging in. It's actually more configuration work to make it view an pre-existing desktop session :)
Remember that X was developed at MIT to run MIT labs, and that X was originally meant for thin clients that accessed programs in much the same way described. This stuff has been possible for a long time. VNCs are actually much easier to use with its own X server in most instances than running on a living one.
