SaveRestore VRAM

VIDEOPMI offers saving and restoring of the video buffer of SaveSize for 
each mode and is internally aware of the type of VRAM access it has to 
perform. The parameters taken into consideration when addressing the VRAM 
are BufferAddress, ApertureSize, and SaveSize. See [ModeInfo] section in 
PMI Sections. 

If ApertureSize is equal to or greater than SaveSize, direct linear access 
to the BufferAddress is assumed. If this is not the case, the SetBank 
function is necessary in order to save and restore the entire on-screen 
VRAM. Granularity of a bank is assumed to be the ApertureSize. SaveSize 
should be set to reflect the logical line length programmed by the current 
mode, rather than just horizontal resolution.