Editing PL/M

{{Short description|Programming language for microcomputers based on PL/1 and XPL}}
{{Use dmy dates|date=January 2020|cs1-dates=y}}
{{Infobox programming language
 | name                   = PL/M
 | paradigm               = 
 | released               = {{Start date|1973|df=yes}}<ref name="Shustek_2016"/><ref name="Kildall_1993"/> 
 | developer              = [[Gary Kildall]]<ref name="Swaine_2001"/> at [[Microcomputer Applications Associates]]
 | influenced by          = [[PL/I]], [[XPL]]
 | influenced             = [[CP/M]], PLuS
 | website                = 
}}
'''PL/M''', an acronym for '''''P'''rogramming '''L'''anguage for '''M'''icrocomputers'',<ref name="Shustek_2016"/><ref name="Kildall_1993"/> is a high-level [[programming language|language]] conceived and developed by [[Gary Kildall]] in 1973 for [[Hank Smith (Intel)|Hank Smith]] at [[Intel]] for the [[Intel 8008]]. It was later expanded for the newer [[Intel 8080]].

The 8080 had enough power to run the PL/M compiler, but lacked a suitable form of [[mass storage]]. In an effort to port the language from the [[PDP-10]] to the 8080, Kildall used PL/M to write a [[disk operating system]] that allowed a [[floppy disk]] to be used. This was the basis of [[CP/M]].

==History==
Kildall was working at the [[Naval Postgraduate School]] in [[Monterey, California]] in 1973 when he received funds to equip a computer lab, first with [[MCS-4]]-based SIM4 and, a year later, the [[Intel 8008]]-based [[Intel Intellec 8]].{{sfn|Kildall|1993|p=48}} As part of his employment, Kildall was allowed to spend one day a week on his own projects, but soon found himself spending much more than that living in his [[Volkswagen Type 2|VW Microbus]] in the parking lot of the Intel offices on Bowers Avenue in [[Santa Clara, CA|Santa Clara]].{{sfn|Kildall|1993|p=49}}

One day he went to see Hank Smith, Intel's manager for the tiny microcomputer software department. Kildall explained his idea of making a [[high level language]] for the 8008. Smith didn't understand the concept, so Kildall explained that a programmer could write something like <code>X = Y + Z</code> and the program would convert that into several lines of [[assembler code]] which would perform this operation. Smith then called one of Intel's customers and asked if they might be interested in such a product, and when they expressed their interest, Smith immediately told Kildall to do it.{{sfn|Kildall|1993|p=49}}

Kildall wrote PL/M based on the concepts of the [[XPL]] language, which in turn was based on the syntax and concepts of [[IBM]]'s [[PL/I]]. XPL was explicitly designed to compile PL/I-like programs in a much simpler software system, explicitly for teaching purposes. As Kildall began promoting the language he found that few programmers were interested in it, until he demonstrated that one could write a program of roughly the same size and performance as assembly but in about a tenth of the time.{{sfn|Kildall|1993|p=49}}

PL/M originally ran on large [[PDP-10]] [[mainframe]] computers that would output the final [[machine language]] code on [[punch tape]] which would then be fed into an [[programmable ROM]] burner and then the ROMs would be transferred to the target machine. With the release of the Intellec 8 in 1974, he began an attempt to port the system to this platform to make it "self hosting" and allow programmers to do everything on that platform. Unfortunately, the 8008 had a very small eight entry [[call stack]] that was simply too small for a high-level language.{{sfn|Kildall|1993|p=50}}

This problem was solved with the introduction of the first [[Intel 8080]] in late 1973, which supported a stack of any size in memory.{{sfn|Kildall|1993|p=51}} Intel upgraded the Intellec 8 to the Intellec 8/80 based on the new chip. Although this system had the processing power to run PL/M, it lacked any useful form of [[mass storage]] and adding a useful amount of [[main memory]] was extremely expensive.{{sfn|Kildall|1993|p=52}} Just down the street from Intel, [[Memorex]] had recently introduced a new low-cost [[floppy disk]] drive,{{sfn|Kildall|1993|p=53}} and this in turn prompted [[Alan Shugart]] to start [[Shugart Associates]] and introduce lower-cost drives. Kildall was able to talk [[Finis Conner]], then at Shugart, into giving him one of their older test drives.{{sfn|Kildall|1993|p=54}}

Unfortunately, there was no [[drive controller]] for the Intel systems, and while one was sketched out it was never implemented. After sitting on a shelf for a year, Kildall decided to go ahead and write the software needed to use it in PL/M running on his 8080-emulator on the PDP-10. In 1974 he called a friend from the [[University of Washington]], John Torode, who built a controller for the 8080. After a few months the system was running, and Kildall loaded the driver and it ran the first time and displayed the prompt.{{sfn|Kildall|1993|p=55}}

During the summer of 1975, Kildall was working as a consultant at [[Signetics]], who asked him to port PL/M to their [[Signetics 2650]]. This resulted in the '''PLuS''' language. The 2650 "bombed" in the market and Signetics gave up on it within a year, deciding to license the [[Fairchild F8]] instead. While working there he met [[Jim Warren (computer specialist)|Jim Warren]], another consultant who was also setting up the new minicomputer-oriented magazine, ''[[Dr. Dobb's Journal]]''. Warren suggested Kildall put an ad in the magazine under the name of [[CP/M]], and this launched the system into the market.{{sfn|Kildall|1993|p=58}}

==Overview==
The language incorporated ideas from PL/I and XPL,<ref name="Shustek_2016"/><ref name="Kildall_1993"/> and had an integrated [[Macro (computer science)|macro processor]]. As a graduate of the [[University of Washington]] Kildall had used their [[Burroughs B5500]] computer,<ref name="Kildall_1970_UW"/> and as such was aware of the potential of high-level languages such as [[Executive Systems Problem Oriented Language|ESPOL]] for systems programming.

Unlike other contemporary languages such as [[Pascal (programming language)|Pascal]] or [[BASIC]], PL/M had no standard input or output routines. It included features targeted at the low-level hardware specific to the target microprocessors, and as such, it could support direct access to any location in memory, I/O ports and the processor interrupt flags in a very efficient manner. PL/M was the first higher level programming language for microprocessor-based computers and was the original implementation language for those parts of the [[CP/M]] operating system which were not written in assembler. Many Intel and [[Zilog Z80]]-based [[embedded system]]s were programmed in PL/M during the 1970s and 1980s. For instance, the [[firmware]] of the Service Processor component of CISC [[IBM AS/400]] was written in PL/M.

The original PL/M [[compiler]] targeted the [[Intel 8008]].<ref name="Kildall_1974"/> An updated version (PL/M-80) generated code for the [[Intel 8080|8080]] processor, which would also run on the newer [[Intel 8085]] as well as on the Zilog Z80 family (as it is [[backward-compatible]] with the 8080). Later followed compilers for the [[Intel 8048]] and [[Intel 8051]]-microcontroller family (PL/M-51) as well as for the [[Intel 8086|8086 (8088)]] (PL/M-86), [[Intel 80186|80186 (80188)]] and subsequent 8086-based processors, including the advanced [[Intel 80286|80286]] and the 32-bit [[Intel 80386|80386]]. There were also PL/M compilers developed for later microcontrollers, such as the [[Intel 8061]] and 8096 / [[Intel MCS-96|MCS-96]] architecture family (PL/M-96).<ref name="Intel_1983_SH"/>

While some PL/M compilers were "native", meaning that they ran on systems using that same microprocessor, e.g. for the Intel [[ISIS (operating system)|ISIS]] operating system, there were also [[cross compiler]]s, for instance [[PLMX]], which ran on other operating environments such as [[Digital Research]] CP/M, [[Microsoft]]'s [[DOS]], and [[Digital Equipment Corporation]]'s [[OpenVMS|VAX/VMS]].

'''PL/M''' is no longer supported by Intel, but aftermarket tools like PL/M-to-C [[source-code translator]]s exist.{{citation needed|date=January 2024}}

==PL/M sample code==
<syntaxhighlight lang="rexx">
FIND: PROCEDURE(PA,PB) BYTE;
    DECLARE (PA,PB) BYTE;
    /* FIND THE STRING IN SCRATCH STARTING AT PA AND ENDING AT PB */
    DECLARE J ADDRESS,
        (K, MATCH) BYTE;
    J = BACK ;
    MATCH = FALSE;
        DO WHILE NOT MATCH AND (MAXM > J);
        LAST,J = J + 1; /* START SCAN AT J */
        K = PA ; /* ATTEMPT STRING MATCH AT K */
            DO WHILE SCRATCH(K) = MEMORY(LAST) AND
                NOT (MATCH := K = PB);
            /* MATCHED ONE MORE CHARACTER */
            K = K + 1; LAST = LAST + 1;
            END;
        END;
    IF MATCH THEN /* MOVE STORAGE */
        DO; LAST = LAST - 1; CALL MOVER;
        END;
    RETURN MATCH;
    END FIND;
</syntaxhighlight>

==References==
{{Reflist|refs=
<ref name="Shustek_2016">{{cite web |title=In His Own Words: Gary Kildall |author-first=Len |author-last=Shustek |date=2016-08-02 |work=Remarkable People |publisher=[[Computer History Museum]] |url=http://www.computerhistory.org/atchm/in-his-own-words-gary-kildall/ |access-date=2020-02-02 |url-status=live |archive-url=https://web.archive.org/web/20191003055634/https://computerhistory.org/blog/in-his-own-words-gary-kildall/?key=in-his-own-words-gary-kildall |archive-date=2019-10-03}}</ref>
<ref name="Kildall_1993">{{cite book |title=Computer Connections: People, Places, and Events in the Evolution of the Personal Computer Industry |author-first=Gary Arlen |author-last=Kildall |author-link=Gary Kildall |editor-first1=Scott |editor-last1=Kildall |editor-link=Scott Kildall |editor-first2=Kristin |editor-last2=Kildall |orig-date=1993 |date=2016-08-02 |publisher=Kildall Family |type=Manuscript, part 1 |url=http://www.computerhistory.org/atchm/computer-history-museum-license-agreement-for-the-kildall-manuscript/ |access-date=2016-11-17<!-- https://web.archive.org/web/20161117231531/http://www.computerhistory.org/atchm/computer-history-museum-license-agreement-for-the-kildall-manuscript/ http://s3data.computerhistory.org/kildall-p.1-78-publishable-lowres.pdf |archive-url=https://web.archive.org/web/20161117232745/http://s3data.computerhistory.org/kildall-p.1-78-publishable-lowres.pdf |archive-date=2016-11-17 -->}}</ref>
<!-- <ref name="Johnson_2019">{{cite web |title=ISIS, Intellec, PL/M, iRMX, and Intel - 20th century |date=2019-07-21 |author-first=Herb |author-last=Johnson |work=Retrotechnology |url=http://www.retrotechnology.com/dri/isis.html |access-date=2020-01-29 |url-status=live |archive-url=https://web.archive.org/web/20191002192450/http://www.retrotechnology.com/dri/isis.html |archive-date=2019-10-02}}</ref> -->
<ref name="Swaine_2001">{{cite journal |title=Gary Kildall and Collegial Entrepreneurship |author-first=Michael |author-last=Swaine |author-link=Michael Swaine (technical author) |date=2001-06-22 |journal=[[Dr. Dobb's Journal]] |url=https://www.drdobbs.com/architecture-and-design/gary-kildall-and-collegial-entrepreneurs/184410428<!-- http://www.ddj.com/184410428 --> |access-date=2006-11-20 |url-status=live |archive-url=https://web.archive.org/web/20190726193738/http://www.drdobbs.com/architecture-and-design/gary-kildall-and-collegial-entrepreneurs/184410428 |archive-date=2019-07-26}}</ref>
<ref name="Kildall_1970_UW">{{cite web |title=APL\B5500 - The Language And Its Implementation |author-first=Gary Arlen |author-last=Kildall |author-link=Gary Arlen Kildall |date=September 1970 |id=Technical Report 70-09-04 |publisher=[[University of Washington]], Computer Science Group |url=https://www.cs.washington.edu/tr/1970/09/UW-CSE-70-09-04.PDF |access-date=2020-01-29 |url-status=live |archive-url=https://web.archive.org/web/20191220034728/https://dada.cs.washington.edu/research/tr/1970/09/UW-CSE-70-09-04.PDF |archive-date=2019-12-20}}</ref>
<ref name="Intel_1983_SH">{{cite book |title=Software Handbook |chapter=Translators And Utilities For Program Development |page=3-1 |date=1984 |orig-date=1983 |publisher=[[Intel Corporation]] |id=230786-001 |url=http://bitsavers.trailing-edge.com/components/intel/_dataBooks/230786-001_Intel_Software_Handbook_1984.pdf |access-date=2020-01-29 |url-status=live |archive-url=https://web.archive.org/web/20200129010534/http://bitsavers.trailing-edge.com/components/intel/_dataBooks/230786-001_Intel_Software_Handbook_1984.pdf |archive-date=2020-01-29 |quote=[…] A LANGUAGE FOR EVERY NEED […] PL/M is the most popular 8086 language for systems programming and provides the best of both optimal code and high level language capabilities. […] PL/M-51 was the first high level language ever to be introduced for a microcontroller. The [[Intel 8096|8096]] is similarly supported with PL/M-96. […]}}</ref>
<ref name="Kildall_1974">{{cite magazine |title=High-level language simplifies microcomputer programming |author-last=Kildall |author-first=Gary Arlen |author-link=Gary Arlen Kildall |website=[[Electronics (magazine)|Electronics]] |publisher=[[McGraw-Hill Education]] |date=1974-06-27 |pages=103–109 |url=https://www.retrotechnology.com/dri/kildall_highlevel_1974.pdf |access-date=2021-11-14 |url-status=live |archive-url=https://web.archive.org/web/20211114174610/https://www.retrotechnology.com/dri/kildall_highlevel_1974.pdf |archive-date=2021-11-14}}</ref>
}}

==Further reading==
* {{cite book |publisher=[[Intel Corporation]] |date=January 1980 |orig-date=1976 |title=PL/M-80 Programming Manual |id=Doc # 98-268B |url=http://bitsavers.trailing-edge.com/pdf/intel/PLM/9800268B_PLM-80_Programming_Manual_Jan80.pdf |access-date=2020-01-29 |url-status=live |archive-url=https://web.archive.org/web/20191221205639/http://bitsavers.trailing-edge.com/pdf/intel/PLM/9800268B_PLM-80_Programming_Manual_Jan80.pdf |archive-date=2019-12-21}}
* {{cite book |title=MCS-8 Guide to PL/M Programming |date=September 1973 |publisher=[[Intel Corporation]] |url=http://bitsavers.org/components/intel/MCS8/MCS-8_A_Guide_to_PLM_Programming_Sep73.pdf |access-date=2020-02-02 |url-status=live |archive-url=https://web.archive.org/web/20191221205640/http://bitsavers.org/components/intel/MCS8/MCS-8_A_Guide_to_PLM_Programming_Sep73.pdf |archive-date=2019-12-21}}
* {{cite book |title=PL/M 386 Programmer's Guide |publisher=[[RadiSys Corporation]] |date=December 1999 |url=http://www.slac.stanford.edu/grp/cd/soft/rmx/manuals/PLM_386.PDF |access-date=2020-01-29 |url-status=live |archive-url=https://web.archive.org/web/20060814050742/http://www.slac.stanford.edu/grp/cd/soft/rmx/manuals/PLM_386.PDF |archive-date=2006-08-14}} (NB. Includes entire syntax of PL/M in [[Backus–Naur form|BNF]] notation.)
* {{cite book |author-last=McCracken |author-first=Daniel D. |author-link=Daniel D. McCracken |date=1978 |title=A Guide to PL/M Programming for Microcomputer Applications |publisher=[[Pearson Education|Pearson]] / [[Addison-Wesley]]}}
* {{cite web |title=Development of Intel ISIS Operating System - An interview with Ken Burgett |author-first=Ken |author-last=Burgett |date=2017-11-10 |url=https://www.rogerarrick.com/osiris/burgett.txt |access-date=2023-11-25 |url-status=live |archive-url=https://web.archive.org/web/20231124165914/https://www.rogerarrick.com/osiris/burgett.txt |archive-date=2023-11-24}} [https://web.archive.org/web/20231125032320/https://00362628054895325210.googlegroups.com/attach/1cc719e8305ed/burgett.txt?part=0.1&view=1&vt=ANaJVrFYjqMX6NCUFa_l-LUDCL-Mu3EqJS1xO4wZczmxImZg2kP3F8E1qEWYTXI5rHv6URyeMi3pcc1oH5LeyEkzHUSeSnUncsii1D7SyIa5EcFQPzu1fzM][https://web.archive.org/web/20231125121523/https://www.rogerarrick.com/kenburgett/ 2017 Ken Burgett interview about development of intel ISIS Operating System]

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[[Category:Digital Research languages]]
[[Category:PL/I programming language family]]
[[Category:Procedural programming languages]]
[[Category:Programming languages]]
[[Category:Programming languages created in 1972]]
[[Category:Structured programming languages]]
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