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Format of current directory structure (array, 51h bytes [58h for DOS 4.x] per
drive):
Offset  Size    Description
 00h 67 BYTEs   current path as ASCIZ, starting with 'x:\'
 43h    WORD    bit flags
                bit 15: network drive   \ installable file system if both set
                bit 14: physical drive  / invalid drive if neither bit set
                bit 13: JOIN'ed, current path is actual path without JOIN
                        drive letter in path may differ from logical drive name
                bit 12: SUBST'ed, current path is actual path without SUBST
                        drive letter in path may differ from logical drive name
 45h    DWORD   pointer to DOS Disk Block for this drive
---local drives---
 49h    WORD    starting cluster of current directory
                0000h = root, FFFFh never accessed
 4Bh    WORD    ??? seems always to be FFFFh
 4Dh    WORD    ??? seems always to be FFFFh
---network drives---
 49h    DWORD   pointer to a redirector/REDIRIFS record, else FFFFFFFFh
 4Dh    WORD    stored parameter from INT 21/AX=5F03h???
------
 4Fh    WORD    Offset of '\' in current path field representing root directory
                of logical drive (2 if not SUBST'ed or JOIN'ed, otherwise
                number of bytes in SUBST/JOIN path)
---DOS 4.x---
 51h    BYTE    ??? used by network
 52h    DWORD   pointer to IFS driver for this drive, 00000000h if native DOS
 56h    WORD    ???