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Table 1378

Format of Program Segment Prefix (PSP):
Offset	Size	Description	)
 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 #01379)
 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.
BUG:	When shelling out from the Borland Pascal 7.00 IDE, overly-long
	  command lines will not be delimited by a 0Dh character, and the
	  length byte is set to 80h!  A workaround is to always patch in a
	  0Dh at the last position of the command line buffer before scanning
	  the command line.


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  Copyright 2000   by Ralf Brown     Updated Jul 2000