the entire screen. This method enables x11vnc to detect changes on the screen roughly 32 times more quickly than a sequential check would (unless the changes are very small, say only 1 pixel tall.) If the X11 DAMAGE extension is present, x11vnc uses it to provide hints where to focus its polling, thereby finding changes even more quickly and also lowering the system load. Input injection When x11vnc receives user input events (keystrokes, pointer motion, and pointer button clicks) from a VNC viewer, it must inject them synthetically into the X server. The X11 programming interfaces XTestFakeKeyEvent, XTestFakeMotionEvent, and XTestFakeButtonEvent of the XTEST extension are used to achieve this. For non-X11 managed devices (such as the Mac OS X graphics display) different programming interfaces must be used. x11vnc also provides an interface where the user can supply their own input injection program. Interesting uses Often special-purpose systems are built using the X Window System to manage the graphical display. x11vnc can be used to export the system's display for remote VNC access. This enables remote monitoring, control, and troubleshooting of the special-purpose system. Sometimes this saves sending a technician to a remote site or allows users to control equipment from their workstation or laptop. x11vnc is known to have been run on the following types of systems: Electron microscope, MRI and Radiology image analysis system, Power plant and Oil platform management consoles, Materials distribution control, Ship self-defense system testing, NMR systems, Silicon wafer analysis microscope, and Theater and concert lighting control. x11vnc is used to export the X11 displays in embedded systems such as Linux-based PDAs and Home theater PCs. If x11vnc cannot be run on the special-purpose system, sometimes it can be run on a nearby computer and poll the X server frame buffer over the network. This is how proprietary X terminal devices can be accessed via x11vnc. Xvnc emulation Although x11vnc's primary use is for X servers associated with physical graphics hardware, it can also attach to virtual X servers (whose frame buffers exist in RAM only) such as Xvfb or a Sun Ray session. x11vnc has options (-create and -svc) to start Xvfb automatically, possibly as the Unix user that logged in. The interactive response of x11vnc and Xvfb may not be as fast as Xvnc, however this mode enables features that Xvnc does not have, such as SSL encryption and Unix usernames and passwords. Client-side