Format of request block:
Offset	Size	Description	)
 00h	WORD	001Bh
 02h	BYTE	drive number (0=default, 1=A:, ...)
 03h	BYTE	???
 04h	WORD	???
 06h	DWORD	far pointer to data area
 0Ah	WORD	???
 0Ch	DWORD	far pointer to data area
 10h	WORD	buffer for result
SeeAlso: #03424,#03426