Format of DOS 4.0+ data segment subsegment control blocks:
Offset	Size	Description	)
 00h	BYTE	subsegment type (blocks typically appear in this order)
		"D"  device driver
		"E"  device driver appendage
		"I"  IFS (Installable File System) driver
		     (MS-DOS 7) high-loaded drive data table array (see #02603)
		"F"  FILES=  control block storage area (for FILES>5)
		"X"  FCBS=   control block storage area, if present
		"C"  BUFFERS EMS workspace area (if BUFFERS /X option used)
		"B"  BUFFERS=  storage area
		"L"  LASTDRIVE=	 current directory structure array storage area
		"S"  STACKS=  code and data area, if present (see #01634,#01635)
		"T"  INSTALL= transient code
 01h	WORD	paragraph of subsegment start (usually the next paragraph)
 03h	WORD	size of subsegment in paragraphs
 05h  3 BYTEs	unused
 08h  8 BYTEs	for types "D" and "I", base name of file from which the driver
		  was loaded (unused for other types)