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Format of FCB reserved field for DOS 3.x

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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.

See Also:

#01646