Format of FCB reserved field for DOS 3.x:
Offset	Size	Description	)
 18h	BYTE	number of system file table entry for file
 19h	BYTE	attributes
		bits 7,6: 00 = SHARE.EXE not loaded, disk file
			  01 = SHARE.EXE not loaded, character device
			  10 = SHARE.EXE loaded, remote file
			  11 = SHARE.EXE loaded, local file or device
		bits 5-0: low six bits of device attribute word
---SHARE.EXE loaded, local file---
 1Ah	WORD	starting cluster of file on disk
 1Ch	WORD	(DOS 3.x) offset within SHARE of sharing record
		  (see #01637 at AH=52h)
 1Eh	BYTE	file attribute
 1Fh	BYTE	???
---SHARE.EXE loaded, remote file---
 1Ah	WORD	number of sector containing directory entry (see #01352)
 1Ch	WORD	relative cluster within file of last cluster accessed
 1Eh	BYTE	absolute cluster number of last cluster accessed
 1Fh	BYTE	???
---SHARE.EXE not loaded---
 1Ah	BYTE	(low byte of device attribute word AND 0Ch) OR open mode
 1Bh	WORD	starting cluster of file
 1Dh	WORD	number of sector containing directory entry (see #01352)
 1Fh	BYTE	number of directory entry within sector
Note:	if FCB opened on character device, DWORD at 1Ah is set to the address
	  of the device driver header, then the BYTE at 1Ah is overwritten.
SeeAlso: #01646