http://wiki.nox-rhea.org/ Mon, 27 Apr 2026 17:26:28 +0000 FeedCreator 1.8 http://wiki.nox-rhea.org/_media/wiki/dokuwiki.svg http://wiki.nox-rhea.org/ http://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/interrupts/int_21/int_21_00?rev=1673888074&do=diff INT 0x21 - 0x00 - Program Terminate This function is no longer recommended, but can be used by version of DOS before 2.0, see Int 0x21,0x4C and Int 0x21,0x00 Request/Call: reg value descr AH 0x00 anonymous@undisclosed.example.com (Anonymous) Mon, 16 Jan 2023 16:54:34 +0000 http://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/interrupts/int_21/int_21_02?rev=1729859131&do=diff INT 0x21 - 0x02 - Write character to standard output Request/Call: reg value descr AH 0x02 DL Character to output Return: reg descr anonymous@undisclosed.example.com (Anonymous) Fri, 25 Oct 2024 12:25:31 +0000 http://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/interrupts/int_21/int_21_3d?rev=1705261071&do=diff INT 0x21 - 0x3d - Open File or Device Using Handle Request/Call: reg value descr AH 0x3d AL open mode (see below) DS:DX pointer to ASCIIZ file name open mode Bit Descr anonymous@undisclosed.example.com (Anonymous) Sun, 14 Jan 2024 19:37:51 +0000 http://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/interrupts/int_21/int_21_3e?rev=1705252278&do=diff INT 0x21 - 0x3e - Read Close File or Device Using Handle Request/Call: reg value descr AH 0x3e BX file handle Return: CF is cleared : success reg descr AX number of bytes readed CF is set: error reg anonymous@undisclosed.example.com (Anonymous) Sun, 14 Jan 2024 17:11:18 +0000 http://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/interrupts/int_21/int_21_3f?rev=1673888074&do=diff INT 0x21 - 0x3f - Read From File or Device Using Handle Request/Call: reg value descr AH 0x3f BX file handle CX number of bytes to read DS:DX pointer to read buffer Return: CF is cleared : success anonymous@undisclosed.example.com (Anonymous) Mon, 16 Jan 2023 16:54:34 +0000 http://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/interrupts/int_21/int_21_4a?rev=1723540650&do=diff INT 0x21 - 0x4a - Resize Memory Block (DOS 2+) This function : * modifies memory block allocated by int 0x21 - 0x48. * can be used by program to shrink or increase the size of allocated memory Request/Call: reg value descr AH anonymous@undisclosed.example.com (Anonymous) Tue, 13 Aug 2024 09:17:30 +0000 http://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/interrupts/int_21/int_21_4b?rev=1723540666&do=diff INT 0x21 - 0x4b - "EXEC" - Load and/or Execute Program (DOS 2+) Request/Call: reg value descr AH 0x4b AL type of load DS:DX ASCIIz program name (must include extentsion) ES:BX parameter block (see below) anonymous@undisclosed.example.com (Anonymous) Tue, 13 Aug 2024 09:17:46 +0000 http://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/interrupts/int_21/int_21_4c?rev=1723540683&do=diff INT 0x21 - 0x4c - "EXIT" - Terminate with return Code (DOS 2+) Request/Call: reg value descr AH 0x4c AL value return code Return: Nothing Notes & Comments * unless the process is its own parent (see AH=26h, offset 16h in PSP), all open files are closed and all memory belonging to the process is freed anonymous@undisclosed.example.com (Anonymous) Tue, 13 Aug 2024 09:18:03 +0000 http://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/interrupts/int_21/int_21_06_ff?rev=1729859456&do=diff INT 0x21 - 0x06 - Direct console input (Sub Function FFh) Request/Call: reg value descr AH 0x06 DL 0xFF Return: if ZF=1 : no character is available if ZF=0 : character is available in AL reg descr anonymous@undisclosed.example.com (Anonymous) Fri, 25 Oct 2024 12:30:56 +0000 http://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/interrupts/int_21/int_21_06?rev=1729859394&do=diff INT 0x21 - 0x06 - Direct console output Request/Call: reg value descr AH 0x06 DL Character to output (except FFh, see anonymous@undisclosed.example.com (Anonymous) Fri, 25 Oct 2024 12:29:54 +0000 http://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/interrupts/int_21/int_21_09?rev=1705253513&do=diff INT 0x21 - 0x09 - print String This function : * print string ending by '$' Request/Call: reg value descr AH 0x9 DS:DX pointer to string ending with '$' anonymous@undisclosed.example.com (Anonymous) Sun, 14 Jan 2024 17:31:53 +0000 http://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/interrupts/int_21/int_21_25?rev=1705255467&do=diff INT 0x21 - 0x25 - Set Interrupt Vector Request/Call: reg value descr AH 0x25 AL Interrupt vector number DS:DX Pointer to Interrupt handler Return: nothing Notes & Comments * Provides a safe method for changing interrupt vectors anonymous@undisclosed.example.com (Anonymous) Sun, 14 Jan 2024 18:04:27 +0000 http://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/interrupts/int_21/int_21_30?rev=1705703036&do=diff INT 0x21 - 0x30 - Get DOS version (DOS 2+) Request/Call: reg value descr AH 0x30 Return: reg descr AL Major version (2 -> x) AL Minor version (in hundredth decimal) BH 0xFF: indicates MS-DOS, only if OEM vendor chooses to identify anonymous@undisclosed.example.com (Anonymous) Fri, 19 Jan 2024 22:23:56 +0000 http://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/interrupts/int_21/int_21_31?rev=1723368228&do=diff INT 0x21 - 0x31 - Terminate Process and Remain Resident Request/Call: reg value descr AH 0x31 AL 0x?? Exit Code DX 0x?? Memory size in paragraphs to reserve Return: Nothing Notes & Comments * preferred method for Terminate and Stay Resident programs anonymous@undisclosed.example.com (Anonymous) Sun, 11 Aug 2024 09:23:48 +0000 http://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/interrupts/int_21/int_21_34?rev=1723541249&do=diff INT 0x21 - 0x34 - Get Address to DOS Critical Flag INDOS (Undocumented DOS 2.0+) Request/Call: reg value descr AH 0x34 Return: reg descr ES:BX address of a byte indicating whether a DOS call is in progress. No DOS calls should be made if set. anonymous@undisclosed.example.com (Anonymous) Tue, 13 Aug 2024 09:27:29 +0000 http://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/interrupts/int_21/int_21_35?rev=1705255382&do=diff INT 0x21 - 0x35 - Get Interrupt Vector Request/Call: reg value descr AH 0x35 AL Interrupt vector number Return: reg descr ES:BX pointer to interrupt vector Notes & Comments * Standard method for retrieving interrupt vectors anonymous@undisclosed.example.com (Anonymous) Sun, 14 Jan 2024 18:03:02 +0000 http://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/interrupts/int_21/int_21_40?rev=1673888074&do=diff INT 0x21 - 0x40 - Write To File or Device Using Handle Request/Call: reg value descr AH 0x40 BX File Handle CX number of bytes to write, a zero value truncates/extends the file to the current file position anonymous@undisclosed.example.com (Anonymous) Mon, 16 Jan 2023 16:54:34 +0000 http://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/interrupts/int_21/int_21_48?rev=1673888074&do=diff INT 0x21 - 0x48 - Allocate Memory Request/Call: reg value descr AH 0x48 BX number of memory paragraph requested Return: * CF set if error * CF cleared if successful reg descr AX Segment address of allocated memory block (MCB + 1para) anonymous@undisclosed.example.com (Anonymous) Mon, 16 Jan 2023 16:54:34 +0000 http://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/interrupts/int_21/int_21_50?rev=1712557390&do=diff INT 0x21 - 0x50 - Set Current Process ID Undocumented DOS 2.x Request/Call: reg value descr AH 0x50 BX process ID number (process PSP segment Address) Return: Nothing Notes & Comments * the process ID number is actually the segment address of a program's PSP. This is useful for TSR's to access their own file handle table inside their PSP. anonymous@undisclosed.example.com (Anonymous) Mon, 08 Apr 2024 06:23:10 +0000 http://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/interrupts/int_21/int_21_51?rev=1712530982&do=diff INT 0x21 - 0x51 - Get Current Process ID Undocumented DOS 2.x Request/Call: reg value descr AH 0x51 Return: reg descr BX process ID Notes & Comments * The process ID number is actually the segment address of program's PSP. This in conjunction with anonymous@undisclosed.example.com (Anonymous) Sun, 07 Apr 2024 23:03:02 +0000 http://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/interrupts/int_21/int_21_58?rev=1705703542&do=diff INT 0x21 - 0x58 - Get/Set Memory Allocation Strategy Undocumented, DOS 3.0 Request/Call: reg value descr AH 0x30 AL var 00: get strategy code 01: set strategy code BX var strategy code (when AL = 01) 00: first fit (default) anonymous@undisclosed.example.com (Anonymous) Fri, 19 Jan 2024 22:32:22 +0000 http://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/interrupts/int_21/int_21_59?rev=1723540753&do=diff INT 0x21 - 0x59 - Get Extended Error Information (DOS 3+) Request/Call: reg value descr AH 0x59 BX 0x00 00 for version 3.0, 3.1, 3.2 0x_ Return: reg descr AX extended error code (see below) anonymous@undisclosed.example.com (Anonymous) Tue, 13 Aug 2024 09:19:13 +0000 http://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/interrupts/int_21/int_21_62?rev=1723540739&do=diff INT 0x21 - 0x62 - Get PSP address (DOS 3+) Request/Call: reg value descr AH 0x62 Return: reg descr BX Segment address of current process Notes & Comments * this is useful for TSR's to access their own file handles anonymous@undisclosed.example.com (Anonymous) Tue, 13 Aug 2024 09:18:59 +0000 http://wiki.nox-rhea.org/back2root/ibm-pc-ms-dos/interrupts/int_21/start?rev=1723529687&do=diff Int 21h - Generic DOS - WIP * INT 0x21 - 0x00 - Program Terminate * INT 0x21 - 0x02 - Write character to standard output * INT 0x21 - 0x06 - Direct console input (Sub Function FFh) * INT 0x21 - 0x06 - Direct console output * INT 0x21 - 0x09 - print String * INT 0x21 - 0x25 - Set Interrupt Vector * INT 0x21 - 0x30 - Get DOS version (DOS 2+) * INT 0x21 - 0x31 - Terminate Process and Remain Resident * INT 0x21 - 0x34 - Get Address to DOS Critical Flag * INT 0x21 - 0x35 - Get Interrupt V… anonymous@undisclosed.example.com (Anonymous) Tue, 13 Aug 2024 06:14:47 +0000