INT 10 - Tseng ET-4000 BIOS(Basic Input/Output System) A set of standardized calls giving low-level access to the hardware.  The BIOS is the lowest software layer above the actual hardware and serves to insulate programs (and operating systems) which use it from the details of accessing the hardware directly. - GET/SET SCREEN REFRESH RATE
	AH = 12h
	BL = F1h
	AL = subfunction
	    00h set refresh rate
	    01h get refresh rate
	BH = video mode
	    00h	 640x480
	    01h	 800x600
	    02h	 1024x768
	    03h	 1280x1024
	CX = new refresh rate (see #00035) if AL = 00h
Return: AL = 12h if supported
	    CX = current rate (for AL=00h, a changed CX indicates failure)


(Table 00035)
Values for Tseng ET4000 refresh rate:
 CX	640x480	800x600	  1024x768/1280x1024
 00h	60 Hz	 56 Hz	   interlaced
 01h	72 Hz	 60 Hz	   60 Hz
 02h	75 Hz	 72 Hz	   70 Hz
 03h	90 Hz	 75 Hz	   75 Hz
 04h	--	 90 Hz	   --