INT 10 - VIDEO - SAVE/RESTORE VIDEO STATE (PS50+,VGA)
        AH = 1Ch
        AL = function
            00h return state buffer size
                Return: BX = number of 64-byte blocks needed
            01h save video state
                ES:BX -> buffer
            02h restore video state
                ES:BX -> buffer containing previously saved state
        CX = requested states
             bit 0 video hardware
             bit 1 BIOS data areas
             bit 2 color registers and DAC state
             bits 3-15 reserved
Return: AL = 1Ch if function supported
Notes:  many BIOSes corrupt the video registers when saving the state, so a
          program should restore the state immediately after saving it (the
          saved data is uncorrupted)
        the BIOS data area consists of the 96 bytes from 0040h:0049h-00A8h

Format of video hardware state:
Offset  Size    Description
 00h    BYTE    sequencer index register
 01h    BYTE    CRTC index register
 02h    BYTE    graphics controller index register
 03h    BYTE    attribute controller index register
 04h    BYTE    feature controller register
 05h  4 BYTEs   sequencer registers
 09h    BYTE    sequencer register 0
 0Ah 25 BYTEs   CRTC registers 0-8
 23h 16 BYTEs   palette registers 00h-0Fh
 33h  4 BYTEs   attribute registers 10h-13h
 37h  9 BYTEs   graphics controller registers 0-8
 40h    BYTE    CRTC base address (low)
 41h    BYTE    CRTC base address (high)
 42h    BYTE    plane 0 latch
 43h    BYTE    plane 1 latch
 44h    BYTE    plane 2 latch
 45h    BYTE    plane 3 latch

Format of DAC state:
Offset  Size    Description
 00h    BYTE    read/write mode DAC
 01h    BYTE    pixel address
 02h    BYTE    pixel mask
 03h 768 BYTEs  color data (256 triples)
303h    BYTE    color select register

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