Virtual xdim ydim
This optional entry specifies the virtual screen resolution to
be used. xdim must be a multiple of either 8 or 16 for most
drivers, and a multiple of 32 when running in monochrome mode.
The given value will be rounded down if this is not the case.
Video modes which are too large for the specified virtual size
will be rejected. If this entry is not present, the virtual
screen resolution will be set to accommodate all the valid video
modes given in the Modes entry. Some drivers/hardware combina-
tions do not support virtual screens. Refer to the appropriate
driver-specific documentation for details.
ViewPort x0 y0
This optional entry sets the upper left corner of the initial
display. This is only relevant when the virtual screen resolu-
tion is different from the resolution of the initial video mode.
If this entry is not given, then the initial display will be
centered in the virtual display area.