I thought they were completely different. But I just noticed, running Screen Sharing on MacOS that the window titlebar says "pitosalas's X desktop". I thought Screen Sharing on MacOS is a VNC client and so, I am confused.


Not sure what your exact setup on your Mac and possible the other machine is, but:

On Linux, you run xvnc or a similar program, which is both an X server (for X clients, i.e. your desktop apps, to connect to) and a VNC server (for other VNC clients which want to see your screen to connect to). What it shares is a virtual framebuffer.

On a Mac, there's XQuartz, which is also an X server for Mac applications which need to connect one. It's possible that this includes something similar to xvnc when screen sharing is active.

So whatever your concrete situation is, it's very likely there's an X server involved somewhere, which shares its framebuffer via VNC.

And yes, the VNC protocol and X servers are indeed completely different.

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  • Could you comment in general whether a graphic-intensive application would perform better on X or on VNC? – pitosalas Jan 25 '19 at 17:11
  • It's pretty difficult to comment on that in general. The wire protocol of X uses graphics primitives, but modern X applications often use OpenGL anyway, which doesn't work with the basic X protocol. VNC on the other hand transfers changed framebuffer parts. "Graphics intensive" normally means OpenGL, so I'd consider something like virtualgl, which is neither X nor VNC. – dirkt Jan 26 '19 at 17:08

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