INT 21 - DOS 5+ - SET EXECUTION STATE AX = 4B05h DS:DX -> execution state structure (see #01625) Return: CF clear if successful AX = 0000h CF set on error AX = error code (see #01680 at AH=59h/BX=0000h) Note: used by programs which intercept AX=4B00h to prepare new programs for execution (including setting the DOS version number). No DOS, BIOS(Basic Input/Output System) A set of standardized calls giving low-level access to the hardware. The BIOS is the lowest software layer above the actual hardware and serves to insulate programs (and operating systems) which use it from the details of accessing the hardware directly. or other software interrupt may be called after return from this call before commencement of the child process. If DOS is running in the HMAsee High Memory Area, A20(Address line 20) The 80286 and higher CPUs allow addresses in real mode to extend slightly beyond the one megabyte mark, which causes an incompatibility with some older programs which expect such addresses to wrap back to the beginning of the address space. For complete compatibility with the 8088, newer machines thus contain circuitry which permits the twenty-first address line (A20) to be disabled. The CPU then effectively has only twenty address lines in real mode, just as the 8088 does, and addresses which would extend beyond the one megabyte mark wrap to the beginning of the address space. See also High Memory Area, Real Mode. is turned off on return from this call. SeeAlso: AH=4Bh Format of execution state structure: Offset Size Description (Table 01625) 00h WORD reserved (00h) 02h WORD type flags bit 0: program is an .EXE bit 1: program is an overlay 04h DWORDDoubleword; four bytes. Commonly used to hold a 32-bit segment:offset or selector:offset address. pointer to 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. name of program file 08h WORD PSPsee Program Segment Prefix segment of new program 0Ah DWORDDoubleword; four bytes. Commonly used to hold a 32-bit segment:offset or selector:offset address. starting CS:IP(Internet Protocol) The lower level (transport layer) of the TCP/IP protocol suite. See also TCP, TCP/IP. of new program 0Eh DWORDDoubleword; four bytes. Commonly used to hold a 32-bit segment:offset or selector:offset address. program size including PSPsee Program Segment Prefix