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+; TITLE   MSHEAD.ASM -- MS-DOS DEFINITIONS
+PAGE
+; MS-DOS  High-performance operating system for the 8086  version 1.28
+;       by Microsoft MSDOS development group:
+;           Tim Paterson (Ret.)
+;           Aaron Reynolds
+;           Nancy Panners (Parenting)
+;           Mark Zbikowski
+;           Chris Peters (BIOS) (ret.)
+
+; ****************** Revision History *************************
+;          >> EVERY change must noted below!! <<
+;
+; 0.34 12/29/80 General release, updating all past customers
+; 0.42 02/25/81 32-byte directory entries added
+; 0.56 03/23/81 Variable record and sector sizes
+; 0.60 03/27/81 Ctrl-C exit changes, including register save on user stack
+; 0.74 04/15/81 Recognize I/O devices with file names
+; 0.75 04/17/81 Improve and correct buffer handling
+; 0.76 04/23/81 Correct directory size when not 2^N entries
+; 0.80 04/27/81 Add console input without echo, Functions 7 & 8
+; 1.00 04/28/81 Renumber for general release
+; 1.01 05/12/81 Fix bug in `STORE'
+; 1.10 07/21/81 Fatal error trapping, NUL device, hidden files, date & time,
+;               RENAME fix, general cleanup
+; 1.11 09/03/81 Don't set CURRENT BLOCK to 0 on open; fix SET FILE SIZE
+; 1.12 10/09/81 Zero high half of CURRENT BLOCK after all (CP/M programs don't)
+; 1.13 10/29/81 Fix classic "no write-through" error in buffer handling
+; 1.20 12/31/81 Add time to FCB; separate FAT from DPT; Kill SMALLDIR; Add
+;               FLUSH and MAPDEV calls; allow disk mapping in DSKCHG; Lots
+;               of smaller improvements
+; 1.21 01/06/82 HIGHMEM switch to run DOS in high memory
+; 1.22 01/12/82 Add VERIFY system call to enable/disable verify after write
+; 1.23 02/11/82 Add defaulting to parser; use variable escape character Don't
+;               zero extent field in IBM version (back to 1.01!)
+; 1.24 03/01/82 Restore fcn. 27 to 1.0 level; add fcn. 28
+; 1.25 03/03/82 Put marker (00) at end of directory to speed searches
+; 1.26 03/03/82 Directory buffers searched as a circular queue, current buffer
+;               is searched first when possible to minimize I/O
+;      03/03/82 STORE routine optimized to tack on partial sector tail as
+;               full sector write when file is growing
+;      03/09/82 Multiple I/O buffers
+;      03/29/82 Two bugs:  Delete all case resets search to start at beginning
+;               of directory (infinite loop possible otherwise), DSKRESET
+;               must invalidate all buffers (disk and directory).
+; 1.27 03/31/82 Installable device drivers
+;                 Function call 47 - Get pointer to device table list
+;                 Function call 48 - Assign CON AUX LIST
+;      04/01/82 Spooler interrupt (INT 28) added.
+; 1.28 04/15/82 DOS retructured to use ASSUMEs and PROC labels around system
+;               call entries.  Most CS relative references changed to SS
+;               relative with an eye toward putting a portion of the DOS in
+;               ROM.  DOS source also broken into header, data and code pieces
+;      04/15/82 GETDMA and GETVECT calls added as 24 and 32.  These calls
+;               return the current values.
+;      04/15/82 INDOS flag implemented for interrupt processing along with
+;               call to return flag location (call 29)
+;      04/15/82 Volume ID attribute added
+;      04/17/82 Changed ABORT return to user to a long ret from a long jump to
+;               avoid a CS relative reference.
+;      04/17/82 Put call to STATCHK in dispatcher to catch ^C more often
+;      04/20/82 Added INT int_upooler into loop ^S wait
+;      04/22/82 Dynamic disk I/O buffer allocation and call to manage them
+;               call 49.
+;      04/23/82 Added GETDSKPTDL as call 50, similar to GETFATPT(DL), returns
+;               address of DPB
+;      04/29/82 Mod to WRTDEV to look for ^C or ^S at console input when
+;               writting to console device via file I/O.  Added a console
+;               output attribute to devices.
+;      04/30/82 Call to en/dis able ^C check in dispatcher Call 51
+;      04/30/82 Code to allow assignment of func 1-12 to disk files as well
+;               as devices....  pipes, redirection now possible
+;      04/30/82 Expanded GETLIST call to 2.0 standard
+;      05/04/82 Change to INT int_fatal_abort callout int HARDERR.  DOS SS
+;               (data segment) stashed in ES, INT int_fatal_abort routines must
+;               preserve ES.  This mod so HARDERR can be ROMed.
+; 1.29 06/01/82 Installable block and character devices as per 2.0 spec
+;      06/04/82 Fixed Bug in CLOSE regarding call to CHKFATWRT.  It got left
+;               out back about 1.27 or so (oops).  ARR
+; 1.30 06/07/82 Directory sector buffering added to main DOS buffer queue
+; 1.40 06/15/82 Tree structured directories.  XENIX Path Parser MKDIR CHDIR
+;               RMDIR Xenix calls
+; 1.41 06/13/82 Made GETBUFFR call PLACEBUF
+; 1.50 06/17/82 FATs cached in buffer pool, get FAT pointer calls disappear
+;               Frees up lots of memory.
+; 1.51 06/24/82 BREAKDOWN modified to do EXACT one sector read/write through
+;               system buffers
+; 1.52 06/30/82 OPEN, CLOSE, READ, WRITE, DUP, DUP2, LSEEK implemented
+; 1.53 07/01/82 OPEN CLOSE mod for Xenix calls, saves and gets remote dir
+; 1.54 07/11/82 Function calls 1-12 make use of new 2.0 PDB. Init code
+;               changed to set file handle environment.
+; 2.00 08/01/82 Number for IBM release
+;      01/19/83 No environ bug in EXEC
+;      01/19/83 MS-DOS OEM INT 21 extensions (SET_OEM_HANDLER)
+;      01/19/83 Performance bug fix in cooked write to NUL
+;      01/27/83 Growcnt fixed for 32-bits
+;      01/27/83 Find-first problem after create
+; 2.01 02/17/83 International DOS
+; 2.11 08/12/83 Dos split into several more modules for assembly on
+;               an IBM PC
+;
+; *************************************************************
+
+
+SUBTTL        EQUATES
+PAGE
+; Interrupt Entry Points:
+
+; INTBASE:      ABORT
+; INTBASE+4:    COMMAND
+; INTBASE+8:    BASE EXIT ADDRESS
+; INTBASE+C:    CONTROL-C ABORT
+; INTBASE+10H:  FATAL ERROR ABORT
+; INTBASE+14H:  BIOS DISK READ
+; INTBASE+18H:  BIOS DISK WRITE
+; INTBASE+1CH:  END BUT STAY RESIDENT (NOT SET BY DOS)
+; INTBASE+20H:  SPOOLER INTERRUPT
+; INTBASE+40H:  Long jump to CALL entry point
+
+ENTRYPOINTSEG   EQU     0CH
+MAXDIF          EQU     0FFFH
+SAVEXIT         EQU     10
+
+        INCLUDE DOSSYM.ASM
+        INCLUDE DEVSYM.ASM
+
+SUBTTL ^C, terminate/abort/exit and Hard error actions
+PAGE
+;
+; There are three kinds of context resets that can occur during normal DOS
+; functioning:  ^C trap, terminate/abort/exit, and Hard-disk error.  These must
+; be handles in a clean fashion that allows nested executions along with the
+; ability to trap one's own errors.
+;
+; ^C trap - A process may elect to catch his own ^Cs.  This is achieved by
+;           using the $GET_INTERRUPT_VECTOR and $SET_INTERRUPT_VECTOR as
+;           follows:
+;
+;           $GET_INTERRUPT_VECTOR for INT int_ctrl_c
+;           Save it in static memory.
+;           $SET_INTERRUPT_VECTOR for INT int_ctrl_c
+;
+;           The interrupt service routine must preserve all registers and
+;           return carry set iff the operation is to be aborted (via abort
+;           system call), otherwise, carry is reset and the operation is
+;           restarted.  ANY DEVIATION FROM THIS WILL LEAD TO UNRELIABLE
+;           RESULTS.
+;
+;           To restore original ^C processing (done on terminate/abort/exit),
+;           restore INT int_ctrl_c from the saved vector.
+;
+; Hard-disk error -- The interrupt service routine for INT int_fatal_abort must
+;           also preserve registers and return one of three values in AL: 0 and
+;           1 imply retry and ignore (???)  and 2 indicates an abort.  The user
+;           himself is not to issue the abort, rather, the dos will do it for
+;           him by simulating a normal abort/exit system call.  ANY DEVIATION
+;           FROM THIS WILL LEAD TO UNRELIABLE RESULTS.
+;
+; terminate/abort/exit -- The user may not, under any circumstances trap an
+;           abort call.  This is reserved for knowledgeable system programs.
+;           ANY DEVIATION FROM THIS WILL LEAD TO UNRELIABLE RESULTS.
+
+SUBTTL SEGMENT DECLARATIONS
+PAGE
+
+; The following are all of the segments used.  They are declared in the order
+; that they should be placed in the executable
+
+;
+; segment ordering for MSDOS
+;
+
+START           SEGMENT BYTE PUBLIC 'START'
+START           ENDS
+
+CONSTANTS       SEGMENT BYTE PUBLIC 'CONST'
+CONSTANTS       ENDS
+
+DATA            SEGMENT WORD PUBLIC 'DATA'
+DATA            ENDS
+
+CODE            SEGMENT BYTE PUBLIC 'CODE'
+CODE            ENDS
+
+LAST            SEGMENT BYTE PUBLIC 'LAST'
+LAST            ENDS
+
+DOSGROUP    GROUP   CODE,CONSTANTS,DATA,LAST
+
+; The following segment is defined such that the data/const classes appear
+; before the code class for ROMification
+
+START           SEGMENT BYTE PUBLIC 'START'
+                ASSUME  CS:DOSGROUP,DS:NOTHING,ES:NOTHING,SS:NOTHING
+        JMP     DOSINIT
+START           ENDS
+
+
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