INT 10 - VIDEO - Video7 VGA,VEGA VGA - GET MODE AND SCREEN RESOLUTION
AX = 6F04h
Return: AL = current video mode (see AX=6F05h)
BX = horizontal columns (text) or pixels (graphics)
CX = vertical columns (text) or pixels (graphics)

See also: 106F05

106F04 - VIDEO - Video7 VGA,VEGA VGA - GET MODE AND SCREEN RESOLUTION