dosints.txt

DOS核心中断的详细讲解

 01h	BYTE	logical drive number (0=A:)
 02h	WORD	bytes per sector
 04h	BYTE	highest sector number within a cluster
 05h	BYTE	shift count to convert clusters into sectors
 06h	WORD	starting sector number of first FAT
 08h	BYTE	number of copies of FAT
 09h	WORD	number of directory entries
 0Bh	WORD	number of first data sector
 0Dh	WORD	highest cluster number (number of data clusters + 1)
 0Fh	BYTE	sectors per FAT
 10h	WORD	starting sector of directory
 12h	WORD	address of allocation table
Note:	the DOS 1.0 table is the same except that the first and last fields
	  are missing; see INT 21/AH=32h for the DOS 2+ version
SeeAlso: #1260,#3891
--------D-2120-------------------------------
INT 21 - DOS 1+ - NULL FUNCTION FOR CP/M COMPATIBILITY
	AH = 20h
Return: AL = 00h
Note:	corresponds to the CP/M BDOS function "get/set default user
	  (sublibrary) number", which is meaningless under MS-DOS
SeeAlso: AH=18h,AH=1Dh,AH=1Eh,AX=4459h
--------D-2121-------------------------------
INT 21 - DOS 1+ - READ RANDOM RECORD FROM FCB FILE
	AH = 21h
	DS:DX -> opened FCB (see #1210)
Return: AL = status
	    00h successful
	    01h end of file, no data read
	    02h segment wrap in DTA, no data read
	    03h end of file, partial record read
	Disk Tranfer Area filled with record read from file
Notes:	the record is read from the current file position as specified by the
	  random record and record size fields of the FCB
	the file position is not updated after reading the record
	if a partial record is read, it is zero-padded to the full size
	not supported by MS Windows 3.0 DOSX.EXE DOS extender
SeeAlso: AH=14h,AH=22h,AH=27h,AH=3Fh"DOS"
--------D-2122-------------------------------
INT 21 - DOS 1+ - WRITE RANDOM RECORD TO FCB FILE
	AH = 22h
	DS:DX -> opened FCB (see #1210)
	Disk Transfer Area contains record to be written
Return: AL = status
	    00h successful
	    01h disk full
	    02h segment wrap in DTA
Notes:	the record is written to the current file position as specified by the
	  random record and record size fields of the FCB
	the file position is not updated after writing the record
	if the record is located beyond the end of the file, the file is
	  extended but the intervening data remains uninitialized
	if the record only partially fills a disk sector, it is copied to a
	  DOS disk buffer to be written out to disk at a later time
	not supported by MS Windows 3.0 DOSX.EXE DOS extender
SeeAlso: AH=15h,AH=21h,AH=28h,AH=40h
--------D-2123-------------------------------
INT 21 - DOS 1+ - GET FILE SIZE FOR FCB
	AH = 23h
	DS:DX -> unopened FCB (see #1210), wildcards not allowed
Return: AL = status
	    00h successful (matching file found)
		FCB random record field filled with size in records, rounded up
		to next full record
	    FFh failed (no matching file found)
Notes:	not supported by MS Windows 3.0 DOSX.EXE DOS extender
	MS-DOS returns nonsense if the FCB record number field is set to a very
	  large positive number, and status FFh if negative; DR DOS returns the
	  correct file size in both cases
BUG:	APPEND for DOS 3.3+ corrupts DX if the file is not found
SeeAlso: AH=42h
--------D-2124-------------------------------
INT 21 - DOS 1+ - SET RANDOM RECORD NUMBER FOR FCB
	AH = 24h
	DS:DX -> opened FCB (see #1210)
Notes:	computes the random record number corresponding to the current record
	  number and record size, then stores the result in the FCB
	normally used when switching from sequential to random access
	not supported by MS Windows 3.0 DOSX.EXE DOS extender
SeeAlso: AH=21h,AH=27h,AH=42h
--------D-2125-------------------------------
INT 21 - DOS 1+ - SET INTERRUPT VECTOR
	AH = 25h
	AL = interrupt number
	DS:DX -> new interrupt handler
Notes:	this function is preferred over direct modification of the interrupt
	  vector table
	some DOS extenders place an API on this function, as it is not
	  directly meaningful in protected mode
	under DR DOS 5.0+, this function does not use any of the DOS-internal
	  stacks and may thus be called at any time
	Novell NetWare (except the new DOS Requester) monitors the offset of
	  any INT 24 set, and if equal to the value at startup, substitutes
	  its own handler to allow handling of network errors; this introduces
	  the potential bug that any program whose INT 24 handler offset
	  happens to be the same as COMMAND.COM's will not have its INT 24
	  handler installed
SeeAlso: AX=2501h,AH=35h
--------D-2126-------------------------------
INT 21 - DOS 1+ - CREATE NEW PROGRAM SEGMENT PREFIX
	AH = 26h
	DX = segment at which to create PSP (see #1243)
Return: AL destroyed
Notes:	new PSP is updated with memory size information; INTs 22h, 23h, 24h
	  taken from interrupt vector table; the parent PSP field is set to 0
	(DOS 2+) DOS assumes that the caller's CS is the segment of the PSP to
	  copy
SeeAlso: AH=4Bh,AH=50h,AH=51h,AH=55h,AH=62h,AH=67h

Format of Program Segment Prefix (PSP):
Offset	Size	Description	(Table 1243)
 00h  2 BYTEs	INT 20 instruction for CP/M CALL 0 program termination
		the CDh 20h here is often used as a signature for a valid PSP
 02h	WORD	segment of first byte beyond memory allocated to program
 04h	BYTE	(DOS) unused filler
		(OS/2) count of fake DOS version returns
 05h	BYTE	CP/M CALL 5 service request (FAR CALL to absolute 000C0h)
		BUG: (DOS 2+ DEBUG) PSPs created by DEBUG point at 000BEh
 06h	WORD	CP/M compatibility--size of first segment for .COM files
 08h  2 BYTEs	remainder of FAR JMP at 05h
 0Ah	DWORD	stored INT 22 termination address
 0Eh	DWORD	stored INT 23 control-Break handler address
 12h	DWORD	DOS 1.1+ stored INT 24 critical error handler address
 16h	WORD	segment of parent PSP
 18h 20 BYTEs	DOS 2+ Job File Table, one byte per file handle, FFh = closed
 2Ch	WORD	DOS 2+ segment of environment for process (see #1244)
 2Eh	DWORD	DOS 2+ process's SS:SP on entry to last INT 21 call
 32h	WORD	DOS 3+ number of entries in JFT (default 20)
 34h	DWORD	DOS 3+ pointer to JFT (default PSP:0018h)
 38h	DWORD	DOS 3+ pointer to previous PSP (default FFFFFFFFh in 3.x)
		used by SHARE in DOS 3.3
 3Ch	BYTE	DOS 4+ (DBCS) interim console flag (see AX=6301h)
		Novell DOS 7 DBCS interim flag as set with AX=6301h
		(possibly also used by Far East MS-DOS 3.2-3.3)
 3Dh	BYTE	(APPEND) TrueName flag (see INT 2F/AX=B711h)
 3Eh	BYTE	(Novell NetWare) flag: next byte initialized if CEh
		(OS/2) capabilities flag
 3Fh	BYTE	(Novell NetWare) Novell task number if previous byte is CEh
 40h  2 BYTEs	DOS 5+ version to return on INT 21/AH=30h
 42h	WORD	(MSWindows3) selector of next PSP (PDB) in linked list
		Windows keeps a linked list of Windows programs only
 44h	WORD	(MSWindows3) "PDB_Partition"
 46h	WORD	(MSWindows3) "PDB_NextPDB"
 48h	BYTE	(MSWindows3) bit 0 set if non-Windows application (WINOLDAP)
 49h	BYTE	unused by DOS versions <= 6.00
 4Ch	WORD	(MSWindows3) "PDB_EntryStack"
 4Eh  2 BYTEs	unused by DOS versions <= 6.00
 50h  3 BYTEs	DOS 2+ service request (INT 21/RETF instructions)
 53h  2 BYTEs	unused in DOS versions <= 6.00
 55h  7 BYTEs	unused in DOS versions <= 6.00; can be used to make first FCB
		  into an extended FCB
 5Ch 16 BYTEs	first default FCB, filled in from first commandline argument
		overwrites second FCB if opened
 6Ch 16 BYTEs	second default FCB, filled in from second commandline argument
		  overwrites beginning of commandline if opened
 7Ch  4 BYTEs	unused
 80h 128 BYTEs	commandline / default DTA
		command tail is BYTE for length of tail, N BYTEs for the tail,
		  followed by a BYTE containing 0Dh
Notes:	in DOS v3+, the limit on simultaneously open files may be increased by
	  allocating memory for a new open file table, filling it with FFh,
	  copying the first 20 bytes from the default table, and adjusting the
	  pointer and count at 34h and 32h.  However, DOS will only copy the
	  first 20 file handles into a child PSP (including the one created on
	  EXEC).
	in an OS/2 DOS box, values of D0h-FEh in the open file table indicate
	  device drivers
	network redirectors based on the original MS-Net implementation use
	  values of 80h-FEh in the open file table to indicate remote files;
	  Novell NetWare also uses values from FEh down to 80h or one more than
	  FILES= (whichever is greater) to indicate remote files (except on
	  OS/2, where is uses CFh down to 80h)
	MS-DOS 5.00 incorrectly fills the FCB fields when loading a program
	  high; the first FCB is empty and the second contains the first
	  parameter
	some DOS extenders place protected-mode values in various PSP fields
	  such as the "parent" field, which can confuse PSP walkers.  Always
	  check either for the CDh 20h signature or that the suspected PSP is
	  at the beginning of a memory block which owns itself (the preceding
	  paragraph should be a valid MCB with "owner" the same as the
	  suspected PSP).
	Novell NetWare updates the fields at offsets 3Eh and 3Fh without
	  checking that a legal PSP segment is current; see AH=50h for further
	  discussion
	for 4DOS and Windows95, the command tail may be more than 126
	  characters; in that case, the length byte will be set to 7Fh (with
	  an 0Dh in the	 127th position at offset FFh), and the first 126
	  characters will be stored in the PSP, with the entire command line
	  in the environment variable CMDLINE; under at least some versions
	  of 4DOS, the byte at offset FFh is *not* set to 0Dh, so there is no
	  terminating carriage return in the PSP's command tail.

Format of environment block:
Offset	Size	Description	(Table 1244)
 00h  N BYTEs	first environment variable, ASCIZ string of form "var=value"
      N BYTEs	second environment variable, ASCIZ string
	...
      N BYTEs	last environment variable, ASCIZ string of form "var=value"
	BYTE	00h
---DOS 3.0+ ---
	WORD	number of strings following environment (normally 1)
      N BYTEs	ASCIZ full pathname of program owning this environment
		other strings may follow
--------D-2127-------------------------------
INT 21 - DOS 1+ - RANDOM BLOCK READ FROM FCB FILE
	AH = 27h
	CX = number of records to read
	DS:DX -> opened FCB (see #1210)
Return: AL = status
	    00h successful, all records read
	    01h end of file, no data read
	    02h segment wrap in DTA, no data read
	    03h end of file, partial read
	Disk Transfer Area filled with records read from file
	CX = number of records read (return AL = 00h or 03h)
Notes:	read begins at current file position as specified in FCB; the file
	  position is updated after reading
	not supported by MS Windows 3.0 DOSX.EXE DOS extender
SeeAlso: AH=21h,AH=28h,AH=3Fh"DOS"
--------D-2128-------------------------------
INT 21 - DOS 1+ - RANDOM BLOCK WRITE TO FCB FILE
	AH = 28h
	CX = number of records to write
	DS:DX -> opened FCB (see #1210)
	Disk Transfer Area contains records to be written
Return: AL = status
	    00h successful
	    01h disk full or file read-only
	    02h segment wrap in DTA
	CX = number of records written
Notes:	write begins at current file position as specified in FCB; the file
	  position is updated after writing
	if CX = 0000h on entry, no data is written; instead the file size is
	  adjusted to be the same as the file position specified by the random
	  record and record size fields of the FCB
	if the data to be written is less than a disk sector, it is copied into
	  a DOS disk buffer, to be written out to disk at a later time
	not supported by MS Windows 3.0 DOSX.EXE DOS extender
SeeAlso: AH=22h,AH=27h,AH=40h,AH=59h/BX=0000h
--------D-2129-------------------------------
INT 21 - DOS 1+ - PARSE FILENAME INTO FCB
	AH = 29h
	AL = parsing options (see #1245)
	DS:SI -> filename string (both '*' and '?' wildcards OK)
	ES:DI -> buffer for unopened FCB
Return: AL = result code
	    00h successful parse, no wildcards encountered
	    01h successful parse, wildcards present
	    FFh failed (invalid drive specifier)
	DS:SI -> first unparsed character
	ES:DI buffer filled with unopened FCB (see #1210)
Notes:	asterisks expanded to question marks in the FCB
	all processing stops when a filename terminator is encountered
	cannot be used with filespecs which include a path (DOS 2+)
	Novell NetWare monitors the result code since an 'invalid drive' may
	  signal an attempt to reconnect a network drive; if there are no
	  connections to the specified drive, NetWare attempts to build a
	  connection and map the drive to the SYS:LOGIN directory
SeeAlso: AH=0Fh,AH=16h,AH=26h

Bitfields for parsing options:
Bit(s)	Description	(Table 1245)
 0	skip leading separators
 1	use existing drive number in FCB if no drive is specified, instead of
	  setting field to zero
 2	use existing filename in FCB if no base name is specified, instead of
	  filling field with blanks
 3	use existing extension in FCB if no extension is specified, instead of
	  filling field with blanks
 4-7	reserved (0)
--------D-212A-------------------------------
INT 21 - DOS 1+ - GET SYSTEM DATE
	AH = 2Ah
Return: CX = year (1980-2099)
	DH = month
	DL = day
---DOS 1.10+---
	AL = day of week (00h=Sunday)
SeeAlso: AH=2Bh"DOS",AH=2Ch,AH=E7h"Novell",INT 1A/AH=04h,INT 2F/AX=120Dh
--------D-212B-------------------------------
INT 21 - DOS 1+ - SET SYSTEM DATE
	AH = 2Bh
	CX = year (1980-2099)
	DH = month
	DL = day
Return: AL = status
	    00h successful
	    FFh invalid date, system date unchanged
Note:	DOS 3.3+ also sets CMOS clock
SeeAlso: AH=2Ah,AH=2Dh,INT 1A/AH=05h
--------D-212C-------------------------------
INT 21 - DOS 1+ - GET SYSTEM TIME
	AH = 2Ch
Return: CH = hour
	CL = minute
	DH = second
	DL = 1/100 seconds
Note:	on most systems, the resolution of the system clock is about 5/100sec,
	  so returned times generally do not increment by 1
	on some systems, DL may always return 00h
SeeAlso: AH=2Ah,AH=2Dh,AH=E7h"Novell",INT 1A/AH=00h,INT 1A/AH=02h,INT 1A/AH=FEh
SeeAlso: INT 2F/AX=120Dh
--------D-212D-------------------------------
INT 21 - DOS 1+ - SET SYSTEM TIME
	AH = 2Dh
	CH = hour
	CL = minute
	DH = second
	DL = 1/100 seconds
Return: AL = result
	    00h successful
	    FFh invalid time, system time unchanged
Note:	DOS 3.3+ also sets CMOS clock
SeeAlso: AH=2Bh"DOS",AH=2Ch,INT 1A/AH=01h,INT 1A/AH=03h,INT 1A/AH=FFh"AT&T"