8514/A Functional Requirements

Determine the existence of the device and the type of display attached.
Trap all the write-only I/O ports, even if the DOS session executes in the foreground (full-screen); otherwise, the device cannot be saved or restored.
No page-fault hook is required because the 8514/A is not a memory-mapped device.
Establish a mechanism with the virtual VGA device driver to manage ownership of the shared device.
Enable the DOS application that is INT 2Fh-aware to save and restore its own video state.
Trap all I/O, whether or not I/O can be virtualized while the DOS session is executing in the background.