Format of XGA subsystem information:
Offset	Size	Description	)
 00h	DWORD	pointer to null-terminated board OEM string
 04h	DWORD	capabilities (see #00072)
 08h	DWORD	pointer to 8KB XGA ROM (or NULL)
 0Ch	DWORD	pointer to the XGA memory mapped registers
 10h	WORD	base address of XGA I/O registers (21x0h)
 12h	DWORD	pointer to start of physical video memory
		(A000h:0000h or B000h:0000h)
 16h	DWORD	physical address of 4MB aperture (or NULL if none)
 1Ah	DWORD	physical address of 1MB aperture (or NULL if none)
 1Eh	DWORD	physical address of 64KB aperture (or NULL if not enabled)
 22h	DWORD	physical address of OEM aperture (or NULL if none)
 26h	WORD	size of OEM aperture in 64KByte units
 28h	DWORD	pointer to list of video modes
		The list is a series of WORDs terminated by FFFFh
 2Ch	WORD	number of 64KB blocks on the board
 2Eh	DWORD	XGA manufacturer ID
		byte 0 POS data index 1
		byte 1 is index 2
		byte 2 is 21xAh index 75h
 32h 206 BYTEs	reserved