Contents of the VGA350.DOC file
VGA SCREEN SIZE
The traditional color/text screen size for IBM terminals has been
640x350 since the PC was introduced in 1981, and that size was maintained up
thru the EGA display. Because the size never varied, most programs were
written to the dimensions of a screen that was invariably 80 character col-
umns by 24 character lines, and the programs never bothered to check the
BIOS data area to see if a different size screen was in use.
With the PS/2 VGA, IBM introduced a different size color/text screen
for the first time, one that is 720x400, and that translates to 80 columns
by 31 lines if you use the EGA size font (typeface). Since IBM introduced
the capacity for user loaded fonts with the EGA, you may occasionally find a
program using EGA sized fonts which runs on the VGA, but doesn't compensate
for the different size screen. This can result in textual graphics which have
a squashed appearance.
IBM provided for a fix for this in their BIOS interface for the VGA,
but they did not make this easily accessible to the user (via the 'mode' com-
mand, for example). And, of course, since it is new with the VGA, the older
EGA programs won't have it in their code.
These three short programs call BIOS service 12H (subservice 30H) via
INT 10H to set the default scan lines for the color/text mode.
VGA350.COM sets the default to 350 lines, VGA400.COM reverses this
and sets it to 400 lines. SETLINES.EXE toggles between the two .
When you set your screen by typeing running one of these programs,
the size set will remain (even thru a subsequent mode reset) until you reboot
or run SETLINES.EXE.
Harve Jay Schiffman