What is the Program Segment Prefix (PSP)? cases, int 21, function 4Ch should be used. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Nowadays, of course, we have DOS function 4Ch which is much easier (and safer) than jumping to location zero in the PSP. So your process is loaded to 1040h:0 and its transient setup takes up, say, 8 KiB. this number by 10h or 16 to get the amount of memory availible. Either function will return the PSP address in register BX.[6]. Alternatively, in .COM programs loaded at offset 100h, one can address the PSP directly just by using the offsets listed above. Thus. offset 81h 97 bytes unformatted command line and/or default DTA. 80h-FEh in the open file table to indicate remote files; Novell NetWare also
It was a wrong question. you need to know about a program running. For example, the following code displays the command line arguments: In DOS 1.x, it was necessary for the CS (Code Segment) register to contain the same segment as the PSP at program termination, thus standard programming practice involved saving the DS register to the stack at program start (since the DS register is loaded with the PSP segment) and terminating the program with a RETF instruction, which would pop the saved segment value off the stack and jump to address 0 of the PSP, which contained an INT 20h instruction. Self Owned means that ownership is given to a never existing program at this very location, so simply storing its own segment handle into that field. Strings are (usually) placed in the environment area via DOS commands like PATH, SET, etc. Personal Software Products (IBM) abbr. Asking for help, clarification, or responding to other answers. The PSP has the following structure: The PSP is most often used to get the command line arguments of a DOS program; for example, the command "FOO.EXE /A /F" executes FOO.EXE with the arguments '/A' and '/F'. In particular, I dont need the command line buffer; this allows me to slash the size of the PSP in half. For other compatible operating systems of the DOS family, see DOS. Notice that the carriage return character is not figured into the length of the command line string. copying the first 20 bytes from the default table, and adjusting the pointer and
To subscribe to this RSS feed, copy and paste this URL into your RSS reader. For 4DOS and Windows95, the command tail may be more than 126 characters; in
Scientifically plausible way to sink a landmass. However, DOS will only copy the first 20 file handles into
Anyway, in DOS v3+ the PSP is not created by the shell usually but by the. In DOS v3+, the limit on simultaneously open files may be
Best way to retrieve K largest elements from large unsorted arrays? 0FFh = availible. Like with an actual TSR with a PSP, you have to take care to close file handles if you DUP them. What is the "FS"/"GS" register intended for? Find centralized, trusted content and collaborate around the technologies you use most. (In fact, I wouldnt be too surprised if the answer were zero, as long as you dont invoke any syscalls as far as the vanilla kernel itself is concerned.) It only takes a minute to sign up. This way, it is possible to pass command lines longer than 126 characters to applications. Programs must not alter any part of the PSP below offset 5Ch. Making statements based on opinion; back them up with references or personal experience. Which of the questions remain open after reading the article I linked? In an OS/2 DOS box, values of D0h-FEh in the open file table indicate device
Some DOS extenders place protected-mode values in various PSP fields such as the
The segment address of the PSP is passed in the DS register when the program is executed. The best answers are voted up and rise to the top, Start here for a quick overview of the site, Detailed answers to any questions you might have, Discuss the workings and policies of this site, Learn more about Stack Overflow the company, It's been a while since I fiddled about with this, but I think my best results were gained by writing my TSR as a device driver and loading it from. ) , Program Segment Prefix Als Programmsegmentprfix (engl. will not be delimited by a 0Dh character, and the length byte is set to 80h! In particular, its program name is read from the (zero-byte-padded) 8 bytes stored in the MCB at offset 8. These are the values normally stored in the interrupt vectors for int 22h, int 23h, and int 24h. Locations 80h through the end of the PSP contain a very important piece of information- the command line parameters typed on the DOS command line along with your program's name. The code above does this in a rather straight-forward manner, using a second loop to finish up when the EOF is reached.
At offset 01h the memory handle (segment) of the PSP of the owning program is recorded. MS-DOS 5.00 incorrectly fills the FCB fields when loading a program high; the Site design / logo 2022 Stack Exchange Inc; user contributions licensed under CC BY-SA. The segment address of the PSP is passed to your program in the ds register. * stack pointer when switching to DOS's own private stack - at the end of overwrites second FCB if opened, second default FCB, filled in from second command line The only (large enough) free space is that directly behind your process, at address 1240h:0. And while I recognise that this makes the question rather fuzzy, I dont necessarily mean the vanilla MS-DOS kernel here, but also clones, emulators (including Windows), programs like MEM, MSD, or anything else that might want to walk the process list and read the contents of PSPs. I uploaded a test program to my repos as testpsps. created with these tools can cause all sorts of problems with standard MSDOS Elle est construite pour chaque processus cr (.com ou .exe), et fait 256 octets de donnes spciales. Pour les Wikipdia en Franais, Zero page (CP/M) The Zero Page (or Base Page) is a data structure used in CP/M systems for programs to communicate with the operating system.
What does function composition being associative even mean? Program Segment Prefix (DOS) abbr. United dictionary of abbreviations and acronyms, MS-DOS This article is about Microsoft MS DOS.
FCB into an extended FCB, first default FCB, filled in from first command line argument argument overwrites beginning of command line if opened. For normal using this particular PSP. Field number two contains a value which points at the last paragraph allocated to your program By subtracting the address of the PSP from this value, you can determine the amount of memory allocated to your program (and quit if there is insufficient memory available). usability help Is it safe to use a license that allows later versions? This is a two-byte pointer which contains the segment address of the environment storage area. Code completion isnt magic; it just feels that way (Ep. a DOS function call, SS:SP is restored from this address. offset 2Eh the DWORD at PSP+2Eh is used by DOS to store the calling process's Why they're here is anyone's guess. EXE files first FCB is empty and the second contains the first parameter. (which may not be the same as the real end of RAM). This is still considerably faster than manipulating the data one byte at a time. by SHARE in DOS 3.3, DOS 4+ (DBCS) interim console flag (see AX=6301h), (APPEND) TrueName flag (see INT 2F/AX=B711h), (Novell NetWare) flag: next byte initialized if CEh, (Novell NetWare) Novell task number if previous byte is CEh, DOS 5+ version to return on INT 21/AH=30h, (MSWindows3) selector of next PSP (PDB) in linked list Windows The third field is the first of many "holes" left in the PSP by Microsoft. Announcing the Stacks Editor Beta release! By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. If you load ah with 51h and execute an int 21h instruction, MS-DOS will return the segment address of the current PSP in the bx register. At which point should I expect the system to start acting up? word stored at offset 0BD3h (PC-DOS 3.1 only). should revector these areas to a safe place if you intend to use them. 2. ), As the resident block is self-owned after this (word [MCB segment:1] equal to MCB segment + 1), it shows up like a regular TSR in MEM output. Program Segment Prefix, PSP) bezeichnet man die ersten 256 Byte eines von MS DOS geladenen Programmes. One last requirement, EXTRN symbols must be declared in the same segment so look there at offset 0. offset 18h handle alias table (networking). The PSP is created by DOS for all programs and contains most of the information offset 05h contains a long call to the DOS function dispatcher. Paper Tape Space comp. Planned Schedule Performance abbr. 3. the allocation chain, look backwards through the PSP link addresses until You can change the environment A solid check for system values can consider all values below 50h as indicating a "special" owner. What exactly is Program Segment Prefix (PSP)? The first segment of availible memory is in segment (paragraph) form. We'll ignore these FCBs in the PSP. that case, the length byte will be set to 7Fh (with an 0Dh in the 127th position There isn't much to this program at all. offset 40h 2 byte field points to the segment address of COMMAND.COM's PSP It can also be determined later by using Int 21h function 51h or Int 21h function 62h. Alternatively, in .COM programs loaded at offset 100h, one can address the PSP directly just by using the offsets listed above. On a magnetar, which force would exert a bigger pull on a 10 kg iron chunk? Locations 81h through 97h contain the characters making up the parameter string. workaround is to always patch in a 0Dh at the last position of the command line Retrocomputing Stack Exchange is a question and answer site for vintage-computer hobbyists interested in restoring, preserving, and using the classic computer and gaming systems of yesteryear. However, this may also make software assume that there should be a PSP when there isn't. So changing that transfers ownership (bad hack, but there's no other way). And I'm not sure what. The fourth field is a call to the DOS function dispatcher. Although the PSP is loaded into memory immediately before your program, that doesn't necessarily mean that it appears 100h bytes before your code. This information should not be considered complete, up to date, and is not intended to be used in place of a visit, consultation, or advice of a legal, medical, or any other professional. In 8 bit CP/M versions it is located in the first 256 bytes of memory, hence its name.The equivalent structure in MS DOS Wikipedia, Com-Datei Eine Com Datei ist eine ausfhrbare Datei in CP/M, MS DOS und zu MS DOS kompatiblen Betriebssystemen. non-permanent COMMAND or a multitasking shell, etc. Also you can make PRN go to CON, To find the beginning of Making statements based on opinion; back them up with references or personal experience. CSEE | By storing a copy of the values in the vectors for these interrupts, you can change these vectors so that they point into your own code. Try this under debug and explore the addresses located at these offsets; Remember under debug you will have to backtrack two times. A 32h, 34h * table of number of file handles (to 64k of handles!). All content on this website, including dictionary, thesaurus, literature, geography, and other reference data is for informational purposes only. offset 02h contains the segment-paragraph address of the end of memory as The first field in the PSP contains an int 20h instruction. (name) in which the symbol is actually defined. 1000h *3 - Keep in mind that implementations may differ. Balancing needed bending strength of a wood railing post in concrete with the lifespan due to rot, Detecting a known alarm signal in an audio stream. From offset 0x4e, there are some fields RBIL claims are unused by DOS versions <= 6.00, so maybe I could get away with overwriting them too, but then there are some rather cryptically described as being used by Windows 3. If the executable was a .COM file, this procedure was unnecessary and the program could be terminated merely with a direct INT 20h instruction or else calling INT 21h function 0. Note: locations 80h..FFh are used for the default DTA. shell version of COMMAND.COM has PSP:16H = PSP, which indicates "don't look Many languages scan the environment storage area to find default filename paths and other pieces of default information set up by DOS. Programmable Signal Processor engin. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. There is a place in DOS that gives an "authoritative" answer to the actual question: The function 31h handler enforces a minimum size for the PSP. Did DOS zero out the BSS area when it loaded a program? That is, those files opened only for reading or writing (no seeking). "owner" the same as the suspected PSP). Your environment is loaded to 1000h:0 and spans about 1 KiB. These fields contain the default terminate vector, break vector, and critical error handler vectors. Buried in the PSP, however, are a couple of gems that are worth knowing about. count at 34h and 32h. To learn more, see our tips on writing great answers. It resembles the Zero Page in the CP/M operating system. FCBs are used only with the obsolete DOS v1.0 file handling routines, so they are of little interest to us. Are there subjective mitzvos - that vary from person to person? 464), How APIs can take the pain out of legacy system headaches (Ep. The value 8 is well-known for DOS data structures (first two name bytes contain "SD"), DOS code or excluded UMA ranges ("SC"), or other system usages. uses values from FEh down to 80h or one more than FILES= (whichever is greater)
(Maybe 19, if I want to guard against the odd overflow or off-by-one bug.) It allows to define how memory blocks are to be searched for. create edition script mysql programming 2nd project edit cs
Luckily DOS offers exactly a function for that: Setting allocation strategy. Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, The PSP is a data structure used by DOS to describe processes. What does it do and what is the use of it? Multiply In order to get there you must look at the current PSP. MS DOS An example of MS DOS s command line interface, this one showing that the current directory is the root of drive C Wikipedia, Windows 95 Part of the Microsoft Windows family Wikipedia, SoftRAM Infobox Software name = SoftRAM and SoftRAM95 caption = Packaging claimed that SoftRAM could double your memory developer = Syncronys latest release version = 1995 latest release date = August 1995 operating system = Microsoft Windows genre = Wikipedia, United dictionary of abbreviations and acronyms. You can free your environment but it's too small for your resident to fit in the resulting gap. which * will most often be COMMAND.COM but perhaps may be a secondary a child PSP (including the one created on EXEC). Triviality of vector bundles on affine open subsets of affine space, Connecting Led to push-pull instead of open-drain, How to encourage melee combat when ranged is a stronger option, Man begins work in the Amazon forest as a logger, changes his mind after hallucinating with the locals. 211 | 465). Now consider the same example rewritten to use blocked I/O: 
Otherwise, and assumed by many programs for any non-zero non-8 value, the value is taken as a segment of a program. 
keeps a linked list of Windows programs only, (MSWindows3) bit 0 set if non-Windows application (WINOLDAP), DOS 2+ service request (INT 21/RETF instructions), unused in DOS versions <= 6.00; can be used to make first
Peter Norton's Programmer's Guide to the IBM PC lists all kinds of tricks. Short story about a vortex or wormwhole and something described as a broccoli cat, The launched program can inspect command-line arguments located at to indicate remote files (except on OS/2, where is uses CFh down to 80h). Also take care to transfer the open file handles properly; you want the relocated process to retain its stdout and stderr handles. The environment string area consists of a sequence of zero-terminated strings. The value must be nonzero because zero indicates a free MCB. (instead of occupation of Japan, occupied Japan or Occupation-era Japan), Balancing needed bending strength of a wood railing post in concrete with the lifespan due to rot, Detecting a known alarm signal in an audio stream. lectures | Program Segment Prefix is useful for the program in many ways: More detailed description of PSP can be found in Wikipedia. ; INT 21h subfunction 9 requires '$' to terminate string, ; print message in mess1 (21h subfunction 9), "Upward migration - Part 1: Translators - Using translation programs to move CP/M-86 programs to CP/M and MS-DOS", "Who needs the address wraparound, anyway? The next three fields are used to store special addresses during the execution of a program. drivers. @Raffzahn: How would you avoid leaving such a gap after installation of your resident?
Der Name leitet sich aus der Dateinamenserweiterung .com ab, die fr das englische Wort command (Befehl) steht. If the executable was a .COM file, this procedure was unnecessary and the program could be terminated merely with a direct INT 20h instruction or else calling INT 21h function 0. the CDh 20h signature or that the suspected PSP is at the beginning of a memory Why has climate change not been proven beyond doubt for so long? By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. (The termination happens to close all the process's file handles too.
Connect and share knowledge within a single location that is structured and easy to search. When your program terminates, DOS restores those three vectors from these three fields in the PSP. This program can be reduced in size somewhat using the following code which is only a little more complex: "Program may hook and change the default system reaction to Ctrl-Break" -- The PSP fields are for restoring the parent's handlers during your termination. The 11th field in the PSP is another call to the DOS function dispatcher. This way, it is possible to pass command lines longer than 126 characters to applications. How was the C language ported to architectures with non-power-of-2 word sizes? It can also be determined later by using Int 21h function 51h or Int 21h function 62h. Is "Occupation Japan" idiomatic? Self Owned is a somewhat common way to handle it. offset 5Ch, 65h, 6Ch contain FCB information for use with FCB function calls. the link address is equal to the PSP segment address that it resides in. The memory footprint of every loaded DOS process, including a TSR, includes a data structure known as the Program Segment Prefix, taking 256 bytes. Image of the executable program is loaded from disk to memory right behind the PSP.
At offset 01h the memory handle (segment) of the PSP of the owning program is recorded. MS-DOS 5.00 incorrectly fills the FCB fields when loading a program high; the Site design / logo 2022 Stack Exchange Inc; user contributions licensed under CC BY-SA. The segment address of the PSP is passed to your program in the ds register. * stack pointer when switching to DOS's own private stack - at the end of overwrites second FCB if opened, second default FCB, filled in from second command line The only (large enough) free space is that directly behind your process, at address 1240h:0. And while I recognise that this makes the question rather fuzzy, I dont necessarily mean the vanilla MS-DOS kernel here, but also clones, emulators (including Windows), programs like MEM, MSD, or anything else that might want to walk the process list and read the contents of PSPs. I uploaded a test program to my repos as testpsps. created with these tools can cause all sorts of problems with standard MSDOS Elle est construite pour chaque processus cr (.com ou .exe), et fait 256 octets de donnes spciales. Pour les Wikipdia en Franais, Zero page (CP/M) The Zero Page (or Base Page) is a data structure used in CP/M systems for programs to communicate with the operating system.
What does function composition being associative even mean? Program Segment Prefix (DOS) abbr. United dictionary of abbreviations and acronyms, MS-DOS This article is about Microsoft MS DOS. FCB into an extended FCB, first default FCB, filled in from first command line argument argument overwrites beginning of command line if opened. For normal using this particular PSP. Field number two contains a value which points at the last paragraph allocated to your program By subtracting the address of the PSP from this value, you can determine the amount of memory allocated to your program (and quit if there is insufficient memory available). usability help Is it safe to use a license that allows later versions? This is a two-byte pointer which contains the segment address of the environment storage area. Code completion isnt magic; it just feels that way (Ep. a DOS function call, SS:SP is restored from this address. offset 2Eh the DWORD at PSP+2Eh is used by DOS to store the calling process's Why they're here is anyone's guess. EXE files first FCB is empty and the second contains the first parameter. (which may not be the same as the real end of RAM). This is still considerably faster than manipulating the data one byte at a time. by SHARE in DOS 3.3, DOS 4+ (DBCS) interim console flag (see AX=6301h), (APPEND) TrueName flag (see INT 2F/AX=B711h), (Novell NetWare) flag: next byte initialized if CEh, (Novell NetWare) Novell task number if previous byte is CEh, DOS 5+ version to return on INT 21/AH=30h, (MSWindows3) selector of next PSP (PDB) in linked list Windows The third field is the first of many "holes" left in the PSP by Microsoft. Announcing the Stacks Editor Beta release! By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. If you load ah with 51h and execute an int 21h instruction, MS-DOS will return the segment address of the current PSP in the bx register. At which point should I expect the system to start acting up? word stored at offset 0BD3h (PC-DOS 3.1 only). should revector these areas to a safe place if you intend to use them. 2. ), As the resident block is self-owned after this (word [MCB segment:1] equal to MCB segment + 1), it shows up like a regular TSR in MEM output. Program Segment Prefix, PSP) bezeichnet man die ersten 256 Byte eines von MS DOS geladenen Programmes. One last requirement, EXTRN symbols must be declared in the same segment so look there at offset 0. offset 18h handle alias table (networking). The PSP is created by DOS for all programs and contains most of the information offset 05h contains a long call to the DOS function dispatcher. Paper Tape Space comp. Planned Schedule Performance abbr. 3. the allocation chain, look backwards through the PSP link addresses until You can change the environment A solid check for system values can consider all values below 50h as indicating a "special" owner. What exactly is Program Segment Prefix (PSP)? The first segment of availible memory is in segment (paragraph) form. We'll ignore these FCBs in the PSP. that case, the length byte will be set to 7Fh (with an 0Dh in the 127th position There isn't much to this program at all. offset 40h 2 byte field points to the segment address of COMMAND.COM's PSP It can also be determined later by using Int 21h function 51h or Int 21h function 62h. Alternatively, in .COM programs loaded at offset 100h, one can address the PSP directly just by using the offsets listed above. On a magnetar, which force would exert a bigger pull on a 10 kg iron chunk? Locations 81h through 97h contain the characters making up the parameter string. workaround is to always patch in a 0Dh at the last position of the command line Retrocomputing Stack Exchange is a question and answer site for vintage-computer hobbyists interested in restoring, preserving, and using the classic computer and gaming systems of yesteryear. However, this may also make software assume that there should be a PSP when there isn't. So changing that transfers ownership (bad hack, but there's no other way). And I'm not sure what. The fourth field is a call to the DOS function dispatcher. Although the PSP is loaded into memory immediately before your program, that doesn't necessarily mean that it appears 100h bytes before your code. This information should not be considered complete, up to date, and is not intended to be used in place of a visit, consultation, or advice of a legal, medical, or any other professional. In 8 bit CP/M versions it is located in the first 256 bytes of memory, hence its name.The equivalent structure in MS DOS Wikipedia, Com-Datei Eine Com Datei ist eine ausfhrbare Datei in CP/M, MS DOS und zu MS DOS kompatiblen Betriebssystemen. non-permanent COMMAND or a multitasking shell, etc. Also you can make PRN go to CON, To find the beginning of Making statements based on opinion; back them up with references or personal experience. CSEE | By storing a copy of the values in the vectors for these interrupts, you can change these vectors so that they point into your own code. Try this under debug and explore the addresses located at these offsets; Remember under debug you will have to backtrack two times. A 32h, 34h * table of number of file handles (to 64k of handles!). All content on this website, including dictionary, thesaurus, literature, geography, and other reference data is for informational purposes only. offset 02h contains the segment-paragraph address of the end of memory as The first field in the PSP contains an int 20h instruction. (name) in which the symbol is actually defined. 1000h *3 - Keep in mind that implementations may differ. Balancing needed bending strength of a wood railing post in concrete with the lifespan due to rot, Detecting a known alarm signal in an audio stream. From offset 0x4e, there are some fields RBIL claims are unused by DOS versions <= 6.00, so maybe I could get away with overwriting them too, but then there are some rather cryptically described as being used by Windows 3. If the executable was a .COM file, this procedure was unnecessary and the program could be terminated merely with a direct INT 20h instruction or else calling INT 21h function 0. Note: locations 80h..FFh are used for the default DTA. shell version of COMMAND.COM has PSP:16H = PSP, which indicates "don't look Many languages scan the environment storage area to find default filename paths and other pieces of default information set up by DOS. Programmable Signal Processor engin. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. There is a place in DOS that gives an "authoritative" answer to the actual question: The function 31h handler enforces a minimum size for the PSP. Did DOS zero out the BSS area when it loaded a program? That is, those files opened only for reading or writing (no seeking). "owner" the same as the suspected PSP). Your environment is loaded to 1000h:0 and spans about 1 KiB. These fields contain the default terminate vector, break vector, and critical error handler vectors. Buried in the PSP, however, are a couple of gems that are worth knowing about. count at 34h and 32h. To learn more, see our tips on writing great answers. It resembles the Zero Page in the CP/M operating system. FCBs are used only with the obsolete DOS v1.0 file handling routines, so they are of little interest to us. Are there subjective mitzvos - that vary from person to person? 464), How APIs can take the pain out of legacy system headaches (Ep. The value 8 is well-known for DOS data structures (first two name bytes contain "SD"), DOS code or excluded UMA ranges ("SC"), or other system usages. uses values from FEh down to 80h or one more than FILES= (whichever is greater)
(Maybe 19, if I want to guard against the odd overflow or off-by-one bug.) It allows to define how memory blocks are to be searched for. create edition script mysql programming 2nd project edit cs
Luckily DOS offers exactly a function for that: Setting allocation strategy. Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, The PSP is a data structure used by DOS to describe processes. What does it do and what is the use of it? Multiply In order to get there you must look at the current PSP. MS DOS An example of MS DOS s command line interface, this one showing that the current directory is the root of drive C Wikipedia, Windows 95 Part of the Microsoft Windows family Wikipedia, SoftRAM Infobox Software name = SoftRAM and SoftRAM95 caption = Packaging claimed that SoftRAM could double your memory developer = Syncronys latest release version = 1995 latest release date = August 1995 operating system = Microsoft Windows genre = Wikipedia, United dictionary of abbreviations and acronyms. You can free your environment but it's too small for your resident to fit in the resulting gap. which * will most often be COMMAND.COM but perhaps may be a secondary a child PSP (including the one created on EXEC). Triviality of vector bundles on affine open subsets of affine space, Connecting Led to push-pull instead of open-drain, How to encourage melee combat when ranged is a stronger option, Man begins work in the Amazon forest as a logger, changes his mind after hallucinating with the locals. 211 | 465). Now consider the same example rewritten to use blocked I/O: Otherwise, and assumed by many programs for any non-zero non-8 value, the value is taken as a segment of a program. keeps a linked list of Windows programs only, (MSWindows3) bit 0 set if non-Windows application (WINOLDAP), DOS 2+ service request (INT 21/RETF instructions), unused in DOS versions <= 6.00; can be used to make first
Peter Norton's Programmer's Guide to the IBM PC lists all kinds of tricks. Short story about a vortex or wormwhole and something described as a broccoli cat, The launched program can inspect command-line arguments located at to indicate remote files (except on OS/2, where is uses CFh down to 80h). Also take care to transfer the open file handles properly; you want the relocated process to retain its stdout and stderr handles. The environment string area consists of a sequence of zero-terminated strings. The value must be nonzero because zero indicates a free MCB. (instead of occupation of Japan, occupied Japan or Occupation-era Japan), Balancing needed bending strength of a wood railing post in concrete with the lifespan due to rot, Detecting a known alarm signal in an audio stream. lectures | Program Segment Prefix is useful for the program in many ways: More detailed description of PSP can be found in Wikipedia. ; INT 21h subfunction 9 requires '$' to terminate string, ; print message in mess1 (21h subfunction 9), "Upward migration - Part 1: Translators - Using translation programs to move CP/M-86 programs to CP/M and MS-DOS", "Who needs the address wraparound, anyway? The next three fields are used to store special addresses during the execution of a program. drivers. @Raffzahn: How would you avoid leaving such a gap after installation of your resident? Der Name leitet sich aus der Dateinamenserweiterung .com ab, die fr das englische Wort command (Befehl) steht. If the executable was a .COM file, this procedure was unnecessary and the program could be terminated merely with a direct INT 20h instruction or else calling INT 21h function 0. the CDh 20h signature or that the suspected PSP is at the beginning of a memory Why has climate change not been proven beyond doubt for so long? By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. (The termination happens to close all the process's file handles too.
Connect and share knowledge within a single location that is structured and easy to search. When your program terminates, DOS restores those three vectors from these three fields in the PSP. This program can be reduced in size somewhat using the following code which is only a little more complex: "Program may hook and change the default system reaction to Ctrl-Break" -- The PSP fields are for restoring the parent's handlers during your termination. The 11th field in the PSP is another call to the DOS function dispatcher. This way, it is possible to pass command lines longer than 126 characters to applications. How was the C language ported to architectures with non-power-of-2 word sizes? It can also be determined later by using Int 21h function 51h or Int 21h function 62h. Is "Occupation Japan" idiomatic? Self Owned is a somewhat common way to handle it. offset 5Ch, 65h, 6Ch contain FCB information for use with FCB function calls. the link address is equal to the PSP segment address that it resides in. The memory footprint of every loaded DOS process, including a TSR, includes a data structure known as the Program Segment Prefix, taking 256 bytes. Image of the executable program is loaded from disk to memory right behind the PSP.