INT 21 - DOS 1+ - OPEN FILE USING FCB AH = 0Fh DS:DX -> unopened File Control Block (see below) Return: AL = status 00h successful FFh file not found or access denied Notes: (DOS 3.1+) file opened for read/write in compatibility mode an unopened FCB has the drive, filename, and extension fields filled in and all other bytes cleared not supported by MS Windows 3.0 DOSX.EXE DOS extender DR-DOS checks password attached with AX=4303h SeeAlso: AH=10h,AH=16h,AH=3Dh,4303h Format of File Control Block: Offset Size Description -7 BYTE extended FCB if FFh -6 5 BYTEs reserved -1 BYTE file attribute if extended FCB 00h BYTE drive number (0 = default, 1 = A, etc) 01h 8 BYTEs blank-padded file name 09h 3 BYTEs blank-padded file extension 0Ch WORD current block number 0Eh WORD logical record size 10h DWORD file size 14h WORD date of last write (see AX=5700h) 16h WORD time of last write (see AX=5700h) (DOS 1.1+) 18h 8 BYTEs reserved (see below) 20h BYTE record within current block 21h DWORD random access record number (if record size is > 64 bytes, high byte is omitted) Note: to use an extended FCB, you must specify the address of the FFh flag at offset -7, rather than the address of the drive number field Format of reserved field for DOS 1.0: Offset Size Description 16h WORD location in directory (if high byte = FFh, low byte is device ID) 18h WORD number of first cluster in file 1Ah WORD current absolute cluster number on disk 1Ch WORD current relative cluster number within file (0 = first cluster of file, 1 = second cluster, etc.) 1Eh BYTE dirty flag (00h = not dirty) 1Fh BYTE unused Format of reserved field for DOS 1.10-1.25: Offset Size Description 18h BYTE bit 7: set if logical device bit 6: not dirty bits 5-0: disk number or logical device ID 19h WORD starting cluster number on disk 1Bh WORD current absolute cluster number on disk 1Dh WORD current relative cluster number within file 1Fh BYTE unused Format of reserved field for DOS 2.x: Offset Size Description 18h BYTE bit 7: set if logical device bit 6: set if open??? bits 5-0: ??? 19h WORD starting cluster number on disk 1Bh WORD ??? 1Dh BYTE ??? 1Eh BYTE ??? 1Fh BYTE ??? Format of 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 AH=52h) 1Eh BYTE file attribute 1Fh BYTE ??? ---SHARE.EXE loaded, remote file--- 1Ah WORD number of sector containing directory entry 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 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. Format of reserved field for DOS 5.0: 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 unique sequence number of sharing record 1Eh BYTE file attributes 1Fh BYTE unused??? ---SHARE.EXE loaded, remote file--- 1Ah WORD network handle 1Ch DWORD network ID ---SHARE not loaded, local device--- 1Ah DWORD pointer to device driver header 1Eh 2 BYTEs unused??? ---SHARE not loaded, local file--- 1Ah BYTE extra info bit 7: read-only attribute from SFT bit 6: archive attribute from SFT bits 5-0: high bits of sector number 1Bh WORD starting cluster of file 1Dh WORD low word of sector number containing directory entry 1Fh BYTE number of directory entry within sector .