AH = 52h
Return: ES:BX points to DOS list of lists

List of Lists:
Bytes   Value
-2&-1   Segment of first memory control block
0-3     Pointer to first DOS disk block (see func 36h)
4-7     Partially Unknown. Pointer to a device driver. Maybe first
               resident driver?
8-B     Pointer to CLOCK$ device driver, whether installable or
               resident
C-F     Pointer to actual CON: device driver, whether installable
               or resident
-----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 NUL device
           driver. This is the first device on DOS's linked list
           of device drivers.
-----DOS 3.x
10-11   Maximum bytes/block of any block device (0200h)
12-15   Unknown. Pointer to current directory block????
16-19   Partially Undefined: Pointer to array of drive info:
               51h bytes per drive, starting with A: ...
               00-3F Current path as ASCIIZ, starting with 'x:\'
               40-43 Unknown. I see zeros always
               44    Unknown. Flags? I see 40h, except for
                       entry after last valid entry = 00h
               45-48 Pointer to DOS Disk Block for this drive
               49-4A Unknown. Current track or block? -1 if never
                       accessed.
               4B-4E Unknown. I see -1 always
               4F-52 Unknown. I see 2 always
1A-1D   Unknown. Pointer to data area, maybe including cluster
               allocation table?
1E-1F   Unknown. I see zero always
20      Number of block devices.
21      Value of LASTDRIVE command in CONFIG.SYS (default 5)
22      Beginning (not a pointer. The real beginning!) of NUL device
           driver. This is the first device on DOS's linked list
           of device drivers.
-----------------------------------------------------------