INT 21 - DOS 1+ - CREATE NEW PROGRAM SEGMENT PREFIX AH = 26h DX = segment at which to create PSPsee Program Segment Prefix (see #01378) Return: AL destroyed Notes: new PSPsee Program Segment Prefix is updated with memory size information; INTs 22h, 23h, 24h taken from interrupt vector table; the parent PSPsee Program Segment Prefix field is set to 0 (DOS 2+) DOS assumes that the caller's CS is the segment of the PSPsee Program Segment Prefix to copy BUG: DR DOS 6.0 original releases 05/1991 & 08/1991 had a problem where the segment from which the PSPsee Program Segment Prefix was copied was incorrect so that the PSPsee Program Segment Prefix was not filled correctly and did not contain the command tail. The DR DOS 6.0 BDOS patch "PAT312" English (1992/01/07, XDIR /C: A0C6h) and later "full" rebuilds fix this problem (see INT 21/AX=4452h). SeeAlso: AH=4Bh,AH=50h,AH=51h,AH=55h,AH=62h,AH=67h Format of Program Segment PrefixThe Program Segment Prefix is a 256-byte data area prepended to a program when it is loaded. It contains the command line that the program was invoked with, and a variety of housekeeping information for DOS. See also INT 21h Function 26h. (PSPsee Program Segment Prefix): Offset Size Description (Table 01378) 00h 2 BYTEs INT 20 instruction for CP/M(Control Program for Microcomputers) An early operating system for micros based on the 8-bit Intel 8080 CPU (and later the compatible 8085 and Zilog Z80 CPUs). MSDOS version 1.0 was essentially a clone of CP/M for the Intel 8086. CALL 0 program termination the CDh 20h here is often used as a signature for a valid PSPsee Program Segment Prefix 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(Control Program for Microcomputers) An early operating system for micros based on the 8-bit Intel 8080 CPU (and later the compatible 8085 and Zilog Z80 CPUs). MSDOS version 1.0 was essentially a clone of CP/M for the Intel 8086. CALL 5 service request (FAR CALL to absolute 000C0h) BUG: (DOS 2+ DEBUG) PSPs created by DEBUG point at 000BEh 06h WORD CP/M(Control Program for Microcomputers) An early operating system for micros based on the 8-bit Intel 8080 CPU (and later the compatible 8085 and Zilog Z80 CPUs). MSDOS version 1.0 was essentially a clone of CP/M for the Intel 8086. compatibility--size of first segment for .COM files 08h 2 BYTEs remainder of FAR JMP at 05h 0Ah DWORDDoubleword; four bytes. Commonly used to hold a 32-bit segment:offset or selector:offset address. stored INT 22 termination address 0Eh DWORDDoubleword; four bytes. Commonly used to hold a 32-bit segment:offset or selector:offset address. stored INT 23 control-Break handler address 12h DWORDDoubleword; four bytes. Commonly used to hold a 32-bit segment:offset or selector:offset address. DOS 1.1+ stored INT 24 critical error handler address 16h WORD segment of parent PSPsee Program Segment Prefix 18h 20 BYTEs DOS 2+ Job File TableThe Job File Table (also called Open File Table) stored in a program's PSP which translates handles into SFT numbers. See also INT 21h Function 26h., one byte per file handle, FFh = closed 2Ch WORD DOS 2+ segment of environment for process (see #01379) 2Eh DWORDDoubleword; four bytes. Commonly used to hold a 32-bit segment:offset or selector:offset address. DOS 2+ process's SS:SP on entry to last INT 21 call 32h WORD DOS 3+ number of entries in JFTsee Job File Table (default 20) 34h DWORDDoubleword; four bytes. Commonly used to hold a 32-bit segment:offset or selector:offset address. DOS 3+ pointer to JFTsee Job File Table (default PSPsee Program Segment Prefix:0018h) 38h DWORDDoubleword; four bytes. Commonly used to hold a 32-bit segment:offset or selector:offset address. DOS 3+ pointer to previous PSPsee Program Segment Prefix (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 PSPsee Program Segment Prefix (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 FCBsee File Control Block into an extended FCBsee File Control Block 5Ch 16 BYTEs first default FCBsee File Control Block, filled in from first commandline argument overwrites second FCBsee File Control Block if opened 6Ch 16 BYTEs second default FCBsee File Control Block, filled in from second commandline argument overwrites beginning of commandline if opened 7Ch 4 BYTEs unused 80h 128 BYTEs commandline / default DTAsee Disk Transfer Address 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 PSPsee Program Segment Prefix (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 FCBsee File Control Block fields when loading a program high; the first FCBsee File Control Block is empty and the second contains the first parameter some DOS extenders place protected-mode values in various PSPsee Program Segment Prefix fields such as the "parent" field, which can confuse PSPsee Program Segment Prefix walkers. Always check either for the CDh 20h signature or that the suspected PSPsee Program Segment Prefix is at the beginning of a memory block which owns itself (the preceding paragraph should be a valid MCBsee Memory Control Block with "owner" the same as the suspected PSPsee Program Segment Prefix). Novell NetWare updates the fields at offsets 3Eh and 3Fh without checking that a legal PSPsee Program Segment Prefix 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 PSPsee Program Segment Prefix, 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 PSPsee Program Segment Prefix's command tail. BUG: When shelling out from the Borland Pascal 7.00 IDE(Integrated Drive Electronics) A type of disk drive interface which essentially extends the PCIBM PC's expansion bus all the way to the drive and places the drive controller on the disk drive itself. See also ESDI., 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. Format of environment block: Offset Size Description (Table 01379) 00h N BYTEs first environment variable, ASCIZA NUL-terminated ASCII string. The ASCIZ string "ABC" consists of the four bytes 41h, 42h, 43h, and 00h. Unless otherwise specified, maximum lengths given in the interrupt list do not include the terminating NUL. string of form "var=value" N BYTEs second environment variable, ASCIZA NUL-terminated ASCII string. The ASCIZ string "ABC" consists of the four bytes 41h, 42h, 43h, and 00h. Unless otherwise specified, maximum lengths given in the interrupt list do not include the terminating NUL. string ... N BYTEs last environment variable, ASCIZA NUL-terminated ASCII string. The ASCIZ string "ABC" consists of the four bytes 41h, 42h, 43h, and 00h. Unless otherwise specified, maximum lengths given in the interrupt list do not include the terminating NUL. string of form "var=value" BYTE 00h ---DOS 3.0+ --- WORD number of strings following environment (normally 1) N BYTEs ASCIZA NUL-terminated ASCII string. The ASCIZ string "ABC" consists of the four bytes 41h, 42h, 43h, and 00h. Unless otherwise specified, maximum lengths given in the interrupt list do not include the terminating NUL. full pathname of program owning this environment other strings may follow