INT 2F - xDISK v3.32+ - INSTALLATION CHECK
        AH = DDh
        BX = 7844h ('xD')
        CX = 4953h ('IS')
        DX = 4B3Fh ('K?')
        AL = desired drive (01h-1Ah) or 00h to check for xDISK on any drive
        ES:DI -> 25-byte data buffer (see below)
Return: AX = DDFFh if installed (on specified drive if AL nonzero on entry)
           BX = 87BBh
           DX = B4C0h
           ES:DI buffer filled
        CX,CF destroyed
SeeAlso: INT 21/AX=4404h"xDISK",INT 21/AX=4405h"xDISK"

Format of data buffer:
Offset  Size    Description
 00h    DWORD   pointer to ASCIZ driver signature "xDISK unit: X"
 04h    BYTE    flag: 01h if disk linked to DOS, 00h if unlinked
 05h    BYTE    flag: 01h if write protected, 00h if not
 06h    BYTE    flag: 01h if root directory full, 00h if not
 07h    BYTE    flag: 01h if free space uncompacted, 00h if compacted
 08h    BYTE    resizing state: 00h not resizable, 01h resized, 80h resizable
 09h    BYTE    flag: 01h inelastic resizable disk, 00h elastic
 0Ah  2 BYTEs   reserved
 0Ch    BYTE    flag: 01h collapsed disk, 00h not collapsed
 0Dh    BYTE    flag: 01h using all EMS, 00h some EMS free
 0Eh    BYTE    flag: 01h password enabled, 00h disabled
 0Fh    BYTE    flag: 01h password audio feedback, 00h no feedback
 10h    BYTE    flag: 01h password video feedback, 00h no feedback
 11h    BYTE    flag: 01h confirm changes, 00h no confirmation
 12h    BYTE    flag: 01h terse display, 00h verbose display
 13h    BYTE    flag: 01h click speaker on disk access, 00h no click
 14h    BYTE    flag: 01h flash icon on disk access, 00h no icon flash
 15h    BYTE    FAT entry size: 00h 12-bit, FFh 16-bit
 16h    WORD    count of open files in RAM disk
 18h    BYTE    unused

.