Function  52h   "Used Internally by DOS" - IN-VARS    
 *		Returns a pointer to a set of DOS data variables MCB chain,
		pointer to first of the device\drivers and a pointer to disk
		parameter blocks (first one)
entry   AH      52h 
return	ES:BX	pointer to the DOS list of lists, for disk information. Does not
		access the disk, so information in tables might be incorrect if 
		disk has been changed. Returns a pointer to the following array 
		of longword pointers: 
		Bytes	Value
		-2h,-1h segment of first memory control block 
		00h-03h pointer to first DOS disk block (see function 36h) 
		(continued next page)
Function  52h	"Used Internally by DOS" - IN-VARS
return	ES:BX	Bytes	Value
		04h-07h Pointer to list of DOS file tables
			dword   pointer to next file table 
			word    number of files in this table 
			        35h bytes per file 
			        00h-01h number of file handles referring to 
			                this file 
			        02h-06h unknown 
				07h-0Ah pointer to device\drivers header if
			                character device; pointer to DOS Device 
			                Control Block if block device (see 
			                fn 32h for format) 
			        0Bh-1Fh unknown 
				20h-2Ah filename in Struct -FCB format (no
					path, no period, blank-padded)
                                2Bh-2Ch PSP segment of file's owner 
			        2Dh-30h unknown -  0 always 
			        31h-32h unknown 
			        33h-34h unknown 
		8h-0Bh	pointer to device\driver\CLOCK$-, whether installable
			or resident
		0Ch-0Fh pointer to actual device\driver\CON-, whether
			installable or resident 
Function  52h	"Used Internally by DOS" - IN-VARS
return  ES:BX   Bytes   Value
        (DOS 2.x) 
		10      number of logical drives in system 
		11-12   maximum bytes/block of any block device 
		13-16   unknown 
		17	beginning (not a pointer. The real beginning!) of
			device\driver\NUL-. This is the first device on DOS's
			linked list of device drivers.
        (DOS 3.x) 
		10h-11h maximum bytes/block of any block device (0200h) 
		12h-15h pointer to first disk buffer 
		16h-19h partially undefined: Pointer to array of drive info: 
			51h bytes per drive, starting with A: ... 
			00h-3Fh current path as ASCIIZ, starting with 'x:\ 
		        40h-43h unknown    zeros always 
			44h     unknown    flags? Usually 40h, except for 
			        entry after last valid entry = 00h 
			45h-48h pointer to DOS disk block for this drive 
			49h-4Ah unknown. Current track or block?  
			        -1 if never accessed 
			4Bh-4Eh unknown  -1 always 
			4Fh-52h unknown   2 always 
		1Ah-1Dh pointer to Struct -FCB table (if CONFIG.SYS contains FCBS=)
Function  52h	"Used Internally by DOS" - IN-VARS
return  ES:BX   Bytes   Value
		1Eh-1Fh size of Struct -FCB table
		20h     number of block devices 
		21h     value of LASTDRIVE command in CONFIG.SYS (default 5) 
		22h	beginning (not a pointer. The real beginning!) of
			device\driver\NUL-. This is the first device on DOS's
			linked list of device drivers.
note 1) This call is not supported in OS/2 1.0's DOS Compatibility Box 
     2) Used by DOS 4.0 MEM.EXE, DOS 3.3 ASSIGN.COM, PRINT.COM, SUBST.EXE