> My guess is that, in full screen, memory writes and reads to the VGA are given direct access to the hardware to preserve performances. [sic]
When a DOS VM is in windowed mode, Windows must intercept VGA port I/O and video framebuffer RAM access to a shadow framebuffer and scale/bitblt it to display in its hosted window.
In full screen, exclusive VGA access is possible so it doesn't need to do anything special except restore state on task switching.
Quake would be even faster if it didn't have to support DPMI/Windows and ran in "unreal mode" with virtual memory and I/O port protections disabled.
When a DOS VM is in windowed mode, Windows must intercept VGA port I/O and video framebuffer RAM access to a shadow framebuffer and scale/bitblt it to display in its hosted window.
In full screen, exclusive VGA access is possible so it doesn't need to do anything special except restore state on task switching.
Quake would be even faster if it didn't have to support DPMI/Windows and ran in "unreal mode" with virtual memory and I/O port protections disabled.