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THE DECSYSTEM-20 AT COLUMBIA UNIVERSITY

THE DECSYSTEM-20 AT COLUMBIA UNIVERSITY (1977-1988)

Frank da Cruz and Christine Gianone

The Kermit Project
Columbia University, New York City

December 29, 1988

Copyright © 1988, 2011,
Frank da Cruz and Christine M. Gianone,
All rights reserved.

A nontechnical reminiscence written in 1988 (on the occasion of unplugging Columbia University's last DECSYSTEM-20) for a Digital Press book that was to commemorate DEC's 36-bit machines with a series of articles, but was never published. Minor edits, notes, glossary, links, and HTML formatting added in January, 2001 (plus minor updates from time to time thereafter). For more about the history of computing at Columbia University CLICK HERE.

NOTE: This article was "slashdotted" on Jan 18, 2001, and was read by many people with no idea what it's about. Please bear in mind that this does not purport to be an introduction to or explanation of the influential 36-bit Digital Equipment Corporation (DEC) computers of 1964-1988; rather, it was to be one essay in a book in which other essays would explain the architecture and history of the technology. You can find some topical websites in the LINKS section at the end.

To those for whom the concept of a 36-bit computer seems strange: The very first commercial binary (as opposed to decimal) computer was the IBM 701, which first came online in 1952. It had a 36-bit word. It was followed by the 704 (where the first high-level language, Fortran, was developed in 1953-57, and whose 6-bit BCD character set and 36-bit word explains the 6-character limit on Fortran variable names), the 709, the 7090, and the 7094, all 36 bits. The 36-bit IBM machines were the birthplace of LISP (*) and (arguably) of timesharing (MIT's Compatible Time Sharing System, CTSS, about 1962) and were also the inspiration for DEC's 36-bit PDP-6 (1964), which was the precursor of the PDP-10 and DECSYSTEM-20, which lasted until 1988, the year DEC stopped manufacturing 36-bit machines. Thus 36-bit architectures were prominent (and in many ways dominant) features of the computing landscape from 1952 to 1988: 36 years.

  • List Processing Language, John McCarthy, Stanford University, 1960, still the primary language for artificial intelligence research. LISP's CAR and CDR are IBM 704 concepts: Contents of Address part of Register and Contents of Decrement part of Register — i.e. the left and right halves of the 36-bit word. 36-bit machines with their 18-bit left and right halfwords are perfect LISP machines.

CONTENTS

INTRODUCTION

Until the middle 1970s, Columbia University was firmly entrenched in IBM mainframe OS/360 batch-mode computing. The "Self Service Input/Output" area was proudly named because it was such a great leap forward from the days when students and researchers would meekly present their card decks to the operators and return the next working day for their output — usually to find that their SYSMSG was full of incomprehensible complaints, whose painful decipherment generally led the frustrated user to a missing comma or an extra space in the Job Control Language. Or if the JCL passed inspection then there was a 3-foot thick core dump to curl up with. The SSIO area was a room filled with the mind-numbing cacophony of key punches, the shrieking of IBM's fearsome 1403 printers, the staccato flutter of card readers, card sorters, and interpreters; anxious crowds gathered around the printers, waist deep in discarded output...

Columbia's IBM 360 Model 91, with its 360/75 front end, was one of the biggest, fastest, heaviest, loudest computers in the world when installed in the late 1960s. It covered acres of floor space, and you could look at the magnetic cores through windows in the 6-foot-tall 16K memory boxes, standing in rows that disappeared into the vanishing point. Power was supplied by a rumbling cast-iron motor generator as big as a small truck, and cooling by chilled distilled water (delivered from Deer Park in big glass bottles in wooden crates) pumped through miles of internal plumbing. The CPU control panel had more lights than Times Square. According to legend, among the thousands of toggles and buttons was one whose lethal mission was "Bulb Eject" — certain death to any who pressed it. The control panel now [1988] lies in repose at the Computer Museum in Boston, its hypnotic bulbs dimmed forever (1).

This massive grey and blue Stonehenge, its thick tentacles reaching into the SSIO area, executed ponderous Fortran "codes" for our engineers: twisting bridges; bombarding hapless substances with neutrons; calculating Pi to millions of digits; transforming the earth's magnetic field into music... For our social scientists, it predicted the outcome of the 1956 presidential election with deadly accuracy year after year. For the administrators it spewed forth paychecks and transcripts and accounting statements. And eventually some small corner of it was allocated to our engineering students, applying their laboriously crafted DO-loops and GOTOs to Taylor's series, Simpson's rule, Gauss's quadrature, and Laplace's transform. These students had a relatively simple task: write the program, place it in a sandwich of magic JCL cards, feed the sandwich to the card reader, and collect the resulting output. Many teachers would come to look back upon these simple days with melancholy fondness, though student memories were haunted more by images of slippery fingers gathering up stacks of dropped punch cards.

Terminals began to appear in the early 1970s, at first only a scattering among the shadowy system programmers on Olympus, who were able to converse in arcane languages with "terminal monitors" having names like Milten, Cleo, Orvyl, and Wylbur, and eventually APL and TSO (the former being the "Irtnog" of computer languages, the latter a form of JCL typed at one's terminal). Interacting with the computer was appealing, and yet unsatisfying. The commands were obscure, and computation was still — apart from APL — in the batch.

Enter, in 1975, our first true timesharing system, a DEC PDP-11/50 running the RSTS/E operating system. This was to be a low-budget experiment in genuine interactive computing. Built around the BASIC language, RSTS allowed up to 32 simultaneous users sitting at DECwriters to program, debug, communicate with each other, and generally misbehave — all in real time. RSTS proved enormously popular, and the PDP-11 was soon overwhelmed by eager students.

DEC was chosen because IBM didn't really offer any kind of general purpose interactive timesharing in those days. Compared to the other contenders, the DEC offering was better developed, more mature, and... more fun. And RSTS was chosen as an operating system, rather than, say, UNIX because Version 6 of UNIX was a mighty trusting system that let anyone to do anything. We had the germ of an idea that the system should take some role in protecting users from one another and from themselves. While UNIX offerred little or no facility in this area, RSTS was not without its own weaknesses. Users soon learned that they could assign all the TTYs, so that no one else could use them. Better still, having assigned a TTY, they could run a program on it to masquerade as the login process, faithfully transcribing other people's IDs and passwords into a file, and then dying in a gasp of simulated noise:

  WELCOxE T@\R\~~~~xxx }}}}}~~

Other resourceful users found that if they opened a new file for record-oriented access, they could read records before writing them, picking up old data from other users' deleted files, or the system password file.

And at one point, our system was infested by a cabal of teenagers from a nearby prep school, who had broken in by exploiting a bug in the login process. They had their way with the system for several weeks before they were detected, and it took several days of round-the-clock work to eradicate the numerous trap doors and time bombs they had left behind.

Despite its problems, RSTS proved quite popular, and rapidly became overloaded. The experiment was declared a success, and we began to look about for something bigger and somewhat more sophisticated — BASIC not being exactly the language of choice among computer scientists. This was about when DEC first announced the DECSYSTEM-20 (its logo, all uppercase unlike that of its elder cousin the DECsystem-10, was said to be a slip of the Caps Lock key on the trademark application). Before even looking at the system, we forced the marketing people to drag in some technical help, and quizzed them mercilessly about whether users could assign all the devices, fill up the disk, control-C out of the login process, bombard each other with stupid messages, even whether a file was "scrubbed" when it was deleted. When all seemed to our satisfaction, we took a look at the system.

Wonder and amazement, this computer knows what you're going to type and types it for you! Well, almost. But its attractions were apparent at first glance. If you don't know what to type, then type a question mark, and it lists the possibilities for you. Suddenly "fill-in-the-blank" became more like "multiple choice". Well of course it can tell you! It knows what the choices are, so why shouldn't it tell you??? A question that might have been asked to good advantage ten or fifteen years earlier (visions of veteran system programmers rooting through manual after manual looking for what to type in the next field of some obscure command... a common sight on some machines even to this day). And this "?" was not a highly privileged function (as was ownership of the manual set) — even ORDINARY USERS could employ it. Astonished, we discovered that error messages came out in plain, comprehensible text, rather than 17-digit hexadecimal numbers, so that they could be understood without a "messages and codes" book.

We were sold immediately on the friendliness, the casual attitude, the humor. We didn't know until later that COOKIE (which survives today in UNIX as 'fortune') was not a standard part of the system, and then there was TECO (2):

  @make love
  not WAR?

The DEC-20 was a real, general-purpose timesharing system. It was not built around a particular language, as RSTS was around BASIC. It offered a wide range of compilers, interpreters, text editors, and utilities, reflecting many years of TOPS-10 and TENEX software development. It could absorb not only our RSTS users, but also many of our IBM mainframe Fortran and APL users, and its ease of use would attract many first-time users as well.

Our new DEC-20 arrived June 29, 1977, with TOPS-20 version 1B. Installation was finished by July 26th. Next to the IBM 360/91, and even the DEC PDP-11, it was disappointingly featureless — no lights to speak of, no switches for entering data, no dials, no motors, no pumps... Yet the DEC-20 was infinitely more powerful than the feeble PDP-11. It was equipped with four state-of-the-art RP06 (3) disk drives that could never fill up, and an unbelievable 256K of main memory — words, not bytes! Such a machine would meet our instructional computing requirements for years to come.

Whenever a computer facility gets a new kind of computer, the programmers embark immediately on a furious spate of activity to turn the new system into their beloved old system. As delivered, the DEC-20's only editor (besides an unofficial copy of TECO) was the cryptic, line-oriented EDIT, descended from TOPS-10 SOS. Our users were accustomed to Wylbur, the much less cryptic line editor on our IBM 360/91, so we immediately embarked on writing a version of Wylbur for the DEC-20, to make our IBM users feel more at home.

We began to learn DEC-20 assembly language, and to read the Monitor Calls Reference Manual. We soon discovered that this was a wonderful machine indeed. The instruction set and the repertoire of monitor calls (JSYS's) were astoundingly rich. Included among the monitor calls was a special set, unlike anything we had ever seen: built into the operating system itself were standard functions for conversion between internal and external representations of all the different kinds of data meaningful to the system: numbers in different radices, characters, strings, filenames, directory names, dates and times. Programmers from an earlier era knew that the most difficult and tedious part of writing an interactive program was the prompting, accepting, and validating of data typed in by the user. How many programs written in Fortran have blown up in your face when you typed a letter instead of a digit?...

Best of all, these conversion functions were collected into a single package called the COMND JSYS, developed by Dan Murphy, which allowed programmers to make use of the same "user interface" in their programs as the one in the TOPS-20 Exec: full prompting, editing, help on every field; abbreviation and recognition of keywords and switches; completion of filenames; forgiveness when the user makes a typo, etc.

Programs coded with the COMND JSYS had many virtues. They were friendly, helpful, and consistent. All programs written using COMND worked the same way: type "?" to find out what the commands or options are, type ESC to complete the current field (if possible) and receive a prompt for the next field. People could use the "?" and ESC features liberally to learn their way through a new program, and later, could type terse, abbreviated commands for speed. This approach, called "menu on demand," does not favor the novice over the expert (as menu-oriented systems do), nor the expert over the novice (as do the cryptic, terse command sets of APL or UNIX).

Our new Wylbur-like editor, called "Otto", was written to take full advantage of the COMND JSYS. For all its stubborn limitations, Otto was an immediate success because it allowed IBM mainframe users to move painlessly to the new environment, while simultaneously indoctrinating them in the ways of the DEC-20. Its hidden purpose was to get them hooked, and then frustrate them sufficiently that they would take the time to learn a "real" editor.

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PROGRAMMING LANGUAGES

As the months wore on, we made contact with other DEC 36-bit sites, many of them — Stanford, CMU, MIT, Rutgers, BBN, SRI — with many years of TOPS-10, TENEX, WAITS, or ITS experience, and received from them programs that were to occupy us for years to come. Some were false starts, but others will thrive in some form well into the next century, the legacy of the DEC-10 and -20. From this experience we learned the benefits of sharing, and knew that if we should ever produce anything of general utility, we would share it with others in the same spirit that these institutions shared their work with us.

Our major goal in canvassing these sites was to find out what they did about programming. In conception, the DEC-20 user and system interfaces came as close to perfection as anyone at the time (outside of Xerox PARC) could imagine, but in practice the conception was incompletely realized. Most of the programming languages came directly from TOPS-10, and did not provide access to the TOPS-20 monitor calls or its file system. And yet we were determined that, in this era of structured programming, we would not write systems-level code in assembly language. After brief flirtations with Bliss-10, BCPL, Simula, and even an early Portable C (which was ill suited to the 36-bit architecture), we settled upon Stanford University's Sail as our "offical language," and plunged into a frenzy of the kind of programming incumbent upon every site that gets a new kind of computer: user ID management, resource management, accounting systems, tape conversion programs, ... But several years of devotion to Sail resulted finally in disillusion. There were too many bugs, too much dependence on the runtime system and knowing where it was, too much conversion necessary upon new releases of Sail or of TOPS-20, too many grotesque workarounds to accomplish what would have been natural in assembler — the only language that really understood the machine and the operating system. And from that day forward, all our systems programming was done in assembler.

Like many things, dependence on assembler is good and bad. It was good because it touched a creative nerve — programmers were unfettered, unhampered by the bureaucratic requirements and authoritarian strictures of high-level languages, and they had full access to the machine's instruction set and repertoire of monitor calls, which, on the DEC-20, were a joy to behold. Programming in assembler was just plain fun, and our programmers gleefully turned out millions of lines of code, but with the nagging feeling that there was something sinful in it. This was because of the bad side: assembly language programs are specific to the underlying machine and operating system. What happens to these programs when the machine disappears?

Nevertheless, MACRO was irresistible (MACRO is used here as a generic term, encompassing DEC's MACRO-10 and -20, as well as MIT's Midas and Ralph Gorin's FAIL). Unlike FORTRAN or BASIC or any other language on the DEC-20 (except for Sail, for which we had written a COMND JSYS interface package), MACRO let you write real DEC-20 programs — programs that were helpful, gentle, and forgiving to the user. For assembly language programmers with an IBM 360 background, the machine architecture and instruction set were delightful. A 256K word linear address space (no more BALRs and USINGs!), hundreds of exotic instructions... And the assembler itself allowed for relatively clean, even "structured" programs. For instance, MACRO's in-line literals are almost equivalent to the "begin ... end" blocks of Algol or Pascal, obviating the horrendous spaghetti logic that plagues most assembly language programs. For example, here's an IF-THEN-ELSE construction with multiple statements in each part, and no GOTOs or labels (excuse any mistakes, this is from memory):

        CAIL B, FOO                     ; IF (b >= foo) THEN
         PUSHJ P, [                     ;   BEGIN
                HRROI A, [ASCIZ/.LT./]  ;     message = ".LT.";
                SETOM LESS              ;     less = -1;
                AOS (P)                 ;   END (skip around ELSE-part)
                POPJ P, ]               ; ELSE
         PUSHJ P, [                     ;   BEGIN
                HRROI A, [ASCIZ/.GE./]  ;     message = ".GE.";
                SETZM LESS              ;     less = 0;
                POPJ P, ]               ;   END;
        PSOUT                           ; PRINT message;

Anything within square brackets is a literal; the assembler finds a place to put it, and replaces the literal with the address of that place. Thus, (nearly) any amount of data or code can be placed "in line", rather than in a separate data area. And as you can see from the example, literals can be nested. Other common control structures can be simulated using literals too, such as the CASE statement:

        MOVEM B, @[EXP FOO, BAR, BAZ](A)

This example stores B in FOO, BAR, or BAZ, depending on the value of A. Such an operation would require many lines of code in most other assembly languages, and in most high-level languages.

To cap it off, assembly language programs could be debugged interactively on a symbolic level using "DDT" — not Dichloro-Diphenyl-Trichloroethane, but a "Dynamic Debugging Tool" designed to get the bugs out just as effectively as the real thing, with fewer undesirable side effects (other debugging aids bore similarly insecticidal names, like RAID). With DDT (4) there need be no more poring through thick hex dump printouts, no more inserting print statements and reassembling, etc etc. Its command syntax is a bit obstruse, consisting mostly of cryptic single letters, punctuation marks, tabs, and liberal use of the ESC ("Altmode") character, often doubled. But DDT can do anything. In fact, since it can execute all computer instructions and system services, the creators of MIT's "Incompatible Timesharing System" (ITS) for the PDP-10 used it as their top-level command interpreter. Talk about user-friendly...

The DEC-10/20 instruction set, monitor calls, assembler, and debugger lured many otherwise sensible programmers into prolonged coding sessions, or "hack attacks". A subculture of DEC-10/20 programmers arose, speaking strange words and phrases whose etymologies were mainly traceable to the PDP-10 Hardware Reference Manual. The ingredient added by the hackers (in those days, not a perjorative term) was the pronunciation of mnemonics never intended for human speech organs (AOS, BLT, JRST, ILDB, HRROI), and extension of their meanings into other areas of life (mostly eating). Eventually, this lexicon was collected and codified by Guy Steele of CMU and others as the "Hacker's Jargon," published originally as a file, later expanded into a book (see bibliography).

DEC-10/20 hackers were a small group at first, owing mainly to a paucity of usable documentation. To write a functioning program, one could consult the Hardware Reference Manual, the Monitor Calls Reference Manual, and the MACRO Assembler Reference Manual. But these manuals were just lists of instructions, monitor calls, and pseudo-ops, and did not impart the slightest notion of how to put a program together. In 1981, the situation changed dramatically with the publication of Ralph Gorin's DEC-20 assembly language programming book, and the world was soon overpopulated with undergraduate DEC-20 programmers.

Chris Ryland and Frank had been working on a DEC-20 assembly-language programming guide in 1979-80, which might have become a book had Ralph not beat us to it :-) CLICK HERE to view a plain-text version of it, recently unearthed (Sep 2002), about 220 pages.

Nevertheless, the lack of a coherent set of high-level programming languages, fully integrated with the operating system and file system, was one of the fatal flaws of the DEC-20. This weakness was remedied by DEC in VAX/VMS, where programs written in a variety of languages can call upon common or compatible runtime support, and systems programs can be written in practically any language — even BASIC or FORTRAN.

Many TOPS-10 holdovers ran — and will still run until the final gasp of the last DEC-20 — in "compatibility mode." This meant that programs written in these languages could only access files according to TOPS-10 rules: no long filenames, no funny characters in filenames, no explicit references to directories or generation numbers. In particular, source programs for most programming languages had this restriction: most compilers had not been TOPS-20-ized, and even if they had, LINK had not. Ultimately, this meant that the user had to know about TOPS-10 in order to use TOPS-20, and that high-level language programmers were denied access to many of TOPS-20's features.

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COPING WITH GROWTH

Within a year, our DEC-20 was hopelessly overburdened, with load averages through the roof and the disks filling up regularly. It remained in this condition for another year until we found a way to buy a second machine. Soon that was full too, and in the ensuing years came a third and a fourth, plus a DEC-20 in Columbia's Computer Science department and another in the Teachers College. The Computer Center systems were upgraded by adding memory and disks, and eventually by interconnecting them all with CFS, and installing RA-81 disk drives and an HSC-50. Eventually, all the CPUs were upgraded to 2065's with maximum memory, and there was nothing further we could do to get more performance out of them. Like other DEC-20 loyalists, we had filled our machine room to capacity with DEC-20s and had no room for more. Our only option for expansion would be a new model, with more power in less floor space. For several years, we made periodic trips to Marlboro to discuss a forthcoming machine. There were actually 2 projects.

DOLPHIN began as a high-end system which would offer a truly distributed 36-bit architecture. Large DOLPHINS would sit amid small single-user MINNOWS on a high-bandwidth network. Both DOLPHIN and MINNOW succumbed to problems with technology. DOLPHIN used custom designed Motorola chips that had reliability problems. MINNOW's dense packaging, designed to fit into a VT52 terminal case, coupled with the need for a locally attached RP06 disk drive(!), were its downfall. Ethernet was still years away from commercial use, and the network problem remained as well. [2]

The JUPITER project came along several months after DOLPHIN was canceled. Its design did not incorporate distributed MINNOWs, but did endorse the requirement for a fast centralized processor. It was to be 10+MIPS, and cheap. A long and difficult design process resulted in neither of these goals being met and in 1983 the project was canceled, although portions of it eventually reached the marketplace — the CI, the HSC-50, etc. [2]

LCG management and engineers always assured us on each visit to Marlboro (MA) (sometimes including helicopter and limo rides, plus lodging in "theme" hotels) that the new system was just "18 months away" from announcement, regardless of its code name. The cost of ownership of either system would have been significantly lower than the equivalent number of KLs.

While waiting for the Jupiter to appear, we still needed ways to apportion our existing DEC-20 resources among the users in the fairest way. This had been a concern since early on. The DEC-20, as originally delivered, allowed ordinary users to take over the machine in various ways, making it unusable by everyone else. Users wrote programs to endlessly create self-replicating forks, they assigned all the PTYs and used them to write password stealers, they ran programs in infinite loops that consumed all available CPU cycles, they monopolized scarce terminal lines for long hours, they filled up the batch queues, they bombarded the operators with thousands of spurious tape mount requests, they printed millions of pages of nonsense, etc etc.

As a monitor and exec source site, Columbia was able to make modifications to restrict access to certain resources by certain classes of users, based upon user ID or account string, or by taking over "unused" bits in the capability word. But back in our OS/360 days, we learned the painful lesson that local modifications to operating systems come back to haunt us when new releases appear: it took years to upgrade our heavily modified IBM OS/360 21.0 to 21.8. Therefore we felt obliged to convince DEC that our requirements applied universally. To do this, we went through channels, first submitting Software Performance Report forms, then writing letters, and finally we had a series of meetings with the monitor group in Marlboro.

One product of these meetings was the Access Control Job. This was a customer-supplied task which would be consulted by the monitor whenever users requested access to certain resources. The ACJ could decide whether to grant or deny access based upon the customer site's own criteria. Some of these resources included login, enabling of capabilities, job creation, fork creation, device assignment, batch job submission, tape mounts, structure mounts, directory creation, scheduler class changes, access and connect, etc. This was a great boon to security and resource management.

But the ACJ did not allow us to regulate ongoing consumption of resources. For this we needed to produce a monitoring program to collect per-user statistics on CPU and connect time. Students were granted a weekly budget of connect and CPU time, and received periodic warnings as they approached the cutoff. Even after cutoff, they were allowed to return during off-peak hours to complete their work. The ACJ and Omega allowed our DEC-20s to accommodate a population upwards of 6000 active students on four machines at the peak of the DEC-20 era.

One area was of particular interest to us. Terminals were not connected directly to our DEC-20s, but were switched through a data PBX. Therefore, the DEC-20 did not know that TTY37 (for instance) was terminal number X in room Y of building Z. For reasons of both security and convenience, it was necessary to have this knowledge. If a user was suspected of misbehavior, the staff had to know the user's physical location. And upon job creation, the exec needed to know the terminal type and speed, so the user would not be confused by fractured, jumbled screens. Fortunately, the data PBX had a console terminal that kept a log of connections. This was connected, via an octopus RS-232 cable, to ports on each of the DEC-20s, which kept a database of PBX ports, locations, terminal types, and speeds. This database was used by the ACJ to prevent enabling of capabilities by users at insecure locations like student terminal rooms and dialups, and to prevent login of certain IDs (like Operator and Field Service) altogether outside of the machine room.

The logs kept by the ACJ and Omega included the physical location of the job. These logs enabled us to track down more than a few would-be and actual violators of system security, and other users' privacy.

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NETWORKING

Our first DEC-20 was connected to the IBM 360/91 using DEC's HASP/RJE product, which required its own dedicated DN20 front end. This method of communication was quite painful, requiring the DEC-20 to masquerade as a card reader and line printer to the IBM system. We wrote a series of Sail programs that would build the "magic JCL sandwich" for our users who wanted to send files or submit jobs to the IBM system.

As soon as we got our second DEC-20, we connected it to the first one with DECnet [1980], and then connected this small network with other DEC systems on campus. DECnet was also in use on the Carnegie-Mellon University computer center machines, and so we merged our two DECnets into one with a leased phone line between New York and Pittsburgh, calling the expanded network CCnet [1982] (CC stands for Computer Center, or maybe Carnegie-Columbia). Before long, other institutions joined the network — Stevens Institute of Technology, Case Western Reserve University, New York University, the University of Toledo, and others. The major benefit was sharing of software and programming work by the computer management staffs at these sites, which included DEC-20s, DEC-10s, VAXes, PDP-11s, and other DEC systems. For many years, Columbia and CMU ran a common DEC-20 Galaxy system, jointly developed, which allowed transparent printing over DECnet and spooled print tapes for the Xerox 9700 printer. One of Columbia's DEC-20s served as a mail gateway between CCnet and BITNET, a large academic network based upon IBM mainframe RSCS protocols.

The most important contribution of the DEC-20 to networking was its support for the ARPANET protocols, first NCP and later TCP/IP. For many years, DEC was the only major computer vendor to support these protocols, which were mostly developed on DEC 36-bit machines under TENEX, TOPS-10, and TOPS-20 (and later on VAXes for Berkeley UNIX). In the late 70s and early 80s, the days in which the ARPAnet grew and prospered beyond its original tiny research mandate, it was dominated by DEC 36-bit machines, and many of the basic Internet protocols and procedures were developed in that framework. DEC itself had a DEC-20 on the ARPANET, which allowed major DEC-20 academic and research sites to communicate directly with TOPS-20 engineers, to send bug reports or fixes by e-mail, to transfer files, and so forth. An ARPANET mailing list of TOPS-20 managers was set up by Mark Crispin at Stanford. The mailing list included TOPS-20 developers at DEC, and there was much useful give and take which bypassed the cumbersome SPR procedure.

Locally, our own DEC-20s received NIA20 Ethernet interfaces to replace the awkward and oversized DN20 front ends. Ethernet allowed us to run TCP/IP alongside DECnet, and before long [circa 1982] there was a large campus-wide Ethernet connecting the computer center DEC-20s with departmental systems all over campus, and beyond, thanks to the Computer Science department's Internet membership [1982?], and later [1984?], our own membership in other wide-area TCP/IP based networks like NYSERNET and JVNCNET. Ethernet and TCP/IP even allowed us to discard our HASP RJE link to the IBM mainframes, which by now were on the Ethernet, running TCP/IP code from the University of Wisconsin (later incorporated by IBM into their own product line).

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KERMIT

At the height of the DEC-20's popularity, the demand among students and faculty for user IDs was so great that we could no longer afford to give out perpetual IDs. Instead, instructional IDs were assigned on a per-course basis and then deleted at the end of each semester. Even though files were scrupulously backed up to tape, students were not allowed to request restoral of a previous term's files because of limited tape drive capacity and operator coverage. And even during the term, a student's disk quota (35K — K, not M or G!) was often not sufficient to keep all her files online at the same time.

If DEC-20 users had some kind of removable media, they could take responsibility for managing and archiving their own files. Our first effort in this area involved a little-known product called the DN200, a remote DECnet station that was originally designed to connect 32 terminals and a line printer to the DEC-20 (this product never quite ripened). The DN200 was a PDP-11/34 running some derivative of RSX. Ours — one of a kind — included an 8-inch floppy disk drive. Our plan was to write DN200 software for copying files between the diskettes and the DEC-20 file system. Users would simply insert their own floppies and issue COPY commands to save or restore their files. Fortunately, this project never got off the ground.

But the idea of removable media felt right. Computer users had had it for years in the form of cards, paper tape, or even DEC's own irresistible little back-and-forth-spinning DECtapes, such a fixture on the PDP-8, -9, -10, -11, -12, etc, and sorely missing from the -20. A number of crazy schemes were considered and rejected: letting users send files to the IBM mainframe's card punch, putting a 9-track "self service" tape drive in a public area, writing a program that would convert the user's data to bar codes for printing on our Printronix printers...

Right around this time (1980), 8-bit CP/M microcomputers were appearing on the scene. Even if they weren't good for much else, they could communicate, and they could read and write floppy disks. Put a few of these in public areas, connect them to the DEC-20s, and students would have their removable media — little disks they could take away with them, store and reuse without reliance on the computer center staff. The big question was how to move a file from a big timesharing mainframe to a small personal computer.

We looked at the marketplace and saw that there were a few commercial RS-232 communication packages for micros, but none for the DEC-20. And we had not only DEC-20s and micros to worry about, but also our IBM mainframes. If we bought software to transfer files between the DEC-20 and the Intertec Superbrain (this was the micro we selected, primarily for its tank-like user-proof construction, and despite its silly name), assuming it was available, we would have to buy yet another software package for our IBM mainframe users to do the same. We also had to consider that the Superbrain might not be everyone's micro of choice. Columbia, being a highly decentralized and diverse organization, was likely to have as many different kinds of computers as there were places to put them. If a separate software package was required to connect each unique pair of systems, then we'd find ourselves needing nearly n-squared distinct packages, where n is the number of different kinds of computer systems, with sufficient copies to cover each instance of each system.

Far better to have one software package on each computer, a package that is capable of exchanging data with all the other computers. This reduces the number of required programs to n, which in turn eases the burden on the budget, and makes the user's life a little easier.

All of these questions resulted in the decision to invest in our own programmers rather than the software companies. This way we could have software specifically designed for our own needs. The end result was the Kermit file transfer protocol. Our first Kermit programs were written for the DEC-20 and the Superbrain. Superbrains were placed in public areas to allow students to copy their own files onto floppies, and restore them to the DEC-20 later.

The Kermit protocol was largely influenced by limitations of the DEC-20. The DEC-20, with its PDP-11/40 front end, was designed on the assumption that terminal input comes directly from people sitting at keyboards typing with their fingers at a relatively slow rate — maybe 10 characters per second, tops — whereas large amounts of sustained output can be sent from the computer to the screen. RSX20F, the front end's operating system, therefore allocates small buffers for input and large ones for output. We learned about this the hard way, when we bought our first terminals that included a "transmit screen" function (HDS Concept-100s). As soon as someone tried it, the front end crashed. Similar phenomena were observed with autorepeat keys (as when one of our programmers fell asleep on the keyboard)(5), and again when DEC first released its VT100 terminal: when doing smooth scrolling at 9600 bps the terminal overwhelmed the poor front end with XOFFs and XONs. Later releases of RSX20F coped with these problems in draconian fashion — if input buffers could not be allocated fast enough, the front end would set the line's speed to zero for a second or two! The lesson? Don't send sustained bursts of terminal data into the DEC-20 — it's like trying to make sparrow eat a meatball hero. Kermit's normal packets are therefore quite short, 96 characters maximum — seeds, insects, and worms that a sparrow can digest.

Another peculiarity of the DEC-20 is its sensitivity to control characters. During normal terminal dialog, 17 of the 33 ASCII control characters are used for special purposes — editing, program interruption, flow control, status reporting, signalling end of file, etc. — rather than being accepted as data. Even though a DEC-20 program can open the terminal in "binary mode" to bypass the special processing of these characters, it is not necessarily desirable to do so, because some of these functions could be useful during data transfer. The lesson here is don't send control characters "bare" when transferring data. In fact, the Kermit protocol (in its most basic configuration) sends packets that are strictly short lines of text.

The IBM mainframe (by this time, the 360/91 had been replaced by a 4341 running the VM/CMS operating system) had its own set of peculiarities. Unlike the DEC-20, it used half duplex communication, and used 7 data bits with parity when communicating with the outside ASCII world. This meant that our file transfer protocol would have to be half duplex too, and would require a special mechanism for transmitting 8-bit binary data through a 7-bit communication link. Furthermore, as all communication was through either a 3705 front end (linemode) or an IBM Series/1 (or equivalent, e.g. 7171 or 4994) 3270 protocol converter, both of which treated many of the control characters as commands to be executed immediately, the prohibition on bare control characters in data was reinforced. Reducing the protocol to the lowest common denominator made it work in all cases, but at the expense of efficiency and elegance. Some of the resulting shortcomings were addressed in later years by the addition of long packets and full-duplex sliding-window packet transport to the protocol, as well as a control-character "unprefixing" option.

By happy coincidence, the combined quirks of the DEC-20, the IBM mainframe, and the CP/M microcomputer resulted in a design that would prove adaptable to practically any computer capable of asynchronous communication. A file was first transferred with Kermit protocol on April 29, 1981, by two instances of Kermit-20 running on a single DEC-20, using two serial ports interconnected by a null modem cable.

The idea of sharing our Kermit programs and giving away the source code was a natural outgrowth of our experiences with the community of DEC-10/20 sites. We received so much of our own software from other sites, it was only fair. We included Kermit on our export tapes and submitted it to DECUS. DEC was the first company to recognize Kermit as a tool of widespread value, and publicized it in their Large Systems flyers and newsletters (e.g. Copy-N-Mail, Large Systems News, and EDU). And DEC was the first organization to port Kermit to a new platform — their VT-180 CP/M micro. Because we wanted Kermit software to be shared openly, we did not place our Kermit programs into the public domain. While this might seem contradictory, we felt that by copyrighting the programs, we could prevent them from being taken by entrepreneurs and sold as commercial products, which seemed necessary since we had heard stories of other universities that had been enjoined from using programs which they themselves had written by firms that had taken their public domain work and copyrighted it for themselves.

Because of the widespread distribution of early Kermit programs, along with source code and the protocol specification, sites with other kinds of computers began to write Kermit programs of their own and send them back to us. Some of the early contributions in this vein were DECsystem-10 and VAX/VMS Kermit programs from Stevens Institute of Technology (written in Common Bliss so the code could be shared among TOPS-10, VMS, and P/OS), PDP-11 Kermit from the University of Toledo, and the first bare-bones UNIX Kermit in C from our own Computer Science department. The process continued for many years, resulting in the large collection of Kermit programs you can find today at the Kermit Project Website.

Columbia's Kermit Project used the DEC-20, our CU20B system, as its testbed, librarian, and network home from the beginning until CU20B (our last remaining DEC-20) was switched off in September 1988. The electronic Info-Kermit newsletter was produced and sent out to people on academic and corporate networks all over the world from the DEC-20 using MM, the DEC-20 e-mail program. Those same users could use MM and other e-mail clients for queries and information, and they can also access programs, source code, and documentation through the DEC-20's DECnet and TCP/IP file servers. Even our distribution tapes were originally shipped from our DEC-20s in DUMPER, BACKUP, and ANSI formats.

Until about 1985, DEC-20 Kermit was the "benchmark" against which all other Kermits were to be verified for interoperability. Many new Kermit features were added to DEC-20 Kermit first (server mode, macros, etc). The DEC-20 user interface became the model for most Kermit programs, so millions of people today are using (a remarkable simulation of) the DEC-20's COMND JSYS without knowing it. Long after the DEC-20 faded from the scene, Kermit programs on Windows, UNIX, VMS, MS-DOS, and many other platforms continue to "keep the faith".

Soon after Kermit first appeared, microcomputing became an important force with the introduction of the IBM PC. PCs suddenly became useful general-purpose computers in their own right. In response to urgent requests from Columbia faculty members who had received the first IBM PCs, we hastily produced version 1.0 of IBM PC Kermit and found that Kermit was being used in ways we hadn't anticipated. Rather than use the PC's floppies to store mainframe files, users were doing most of their file creation and manipulation on the PC, and sending the results to the mainframe for archiving and sharing. Kermit had become an early model of distributed processing.

(In later years, after the original Kermit project was canceled by the university, it nevertheless managed to continue until 2011 through various forms of self-funding, and now has moved to its own non-Columbia website at kermitproject.org.)

[ Kermit Project Home ] [ Kermit News issues ] [ Kermit Mailing List Archives ] [ Kermit Newsgroup Archives ]

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SOFTWARE PACKAGES

The DEC 36-bit large systems were the source of some of the most influential and enduring software packages yet written. Here we arbitrarily mention a few of our favorites, with apologies to the hundreds that we have neglected.

Editors

Foremost among the programs created on these systems is the text editor EMACS, created by Richard M. Stallman on ITS, MIT's "Incompatible Timesharing System" for the PDP-10. EMACS embodied the revolutionary concept that the terminal screen should act as a window upon the text being edited, and that any changes to the text should be reflected immediately on the screen. After many years of line-oriented editing (and before that, keypunching) it was hard for us at first to comprehend the power and convenience of a screen editor. There was even discussion about whether we should allow it on our system, as if it were a subsersive influence... "What do we need it for? Every keystroke results in 37 context switches!" etc etc. But soon even the skeptics began to appreciate EMACS for its enormous boost to human productivity, and it quickly became the editor of choice for staff, students, and faculty alike. A cottage industry sprang up at Columbia for adding new terminal types and operations to TECO's database (DEC-10/20 EMACS was written in TECO), as well as new libraries for EMACS itself.

While some may view EMACS and its descendents and relatives as "obsolete" today, compared to GUI editors and word processors, they have one great advantage over the newer editors: they are entirely driven by ordinary ASCII characters (6) (as opposed to function or arrow keys, mouse, etc) so touch typists never have to leave the home keys, and skilled EMACS users can enter and manipulate text faster than experts with other editors can, especially modern but labor-intensive GUI editors. And by restricting the command set to ordinary ASCII characters, EMACS can be used on any platform, no matter how you access it (the workstation's own keyboard and screen, an xterm window, telnet, dialin, rlogin, ssh, etc). Another advantage of EMACS, of course, is its customizability and programmability, but only the older generations of computer users know or care about such things.

Text Formatters

EMACS is an editor for plain text, which means that by itself it cannot ordinarily produce special printing effects like boldface, italics, underlining, math notation, different point sizes, graphics, etc. For that we need — at least in the world of character terminals — a text formatter. EMACS was one of several screen editors for the DEC-20 (TV and TVEDIT were other early contenders), and there were also several text formatters. The DEC-20 comes, of course, with RUNOFF, DEC's standard formatter. RUNOFF is simple, not too powerful, but has the advantage that RUNOFF files are mostly portable among PDP-11's, VAXes, DEC-10s, and DEC-20s. However, RUNOFF is proprietary and therefore not available on non-DEC systems. RUNOFF also has three basic flaws. First, it is strictly procedural, which means that the writer must behave like a programmer, instructing RUNOFF in the minutest detail. Second, it can't do math. And third, it does not support a wide variety of output devices.

These shortcomings are addressed by several text formatters that were developed by users of DEC large systems, and for that matter some of its smaller systems (UNIX, for instance, was originally written for the PDP-7, and later moved to the PDP-11; UNIX nroff and troff are probably offshoots of RUNOFF). Early efforts on 36-bit systems included R and Pub.

Brian Reid, working on a DECsystem-10 for his PhD thesis at CMU, devised a document production language called Scribe, which addressed the procedural element. Where in RUNOFF one must say, "center and underline this word, leave 7 blank lines, indent 4 spaces, etc", in Scribe one says "This is an article, here is the title, here is a section, here is a footnote, here is a bibliographic citation, put this in the index, insert a photograph here and scale it like so, etc" and leaves the stylistic decisions and details up to Scribe, which includes a vast database of document types and publication styles. For example, if you have written an article for the CACM, you can ask Scribe to format it in the CACM's required style. When the CACM rejects it, you simply tell Scribe to redo it in IEEE Computer format, and then submit it there (7).

During its development, Scribe was shared freely with other universities, and there was much give and take between Brian and users all over. When Brian left CMU, however, rights to Scribe were sold to a private company, Unilogic Ltd, which sold it as a commercial product (8). Scribe was a fixture at many DEC-10 and -20 sites, and has been converted from the original Bliss to other languages for use on systems like UNIX, VMS, and even IBM mainframes.

Meanwhile at Stanford, Donald Knuth was planning new editions of his multivolume work, The Art of Computer Programming. But he soon discovered that in the time since his first editions were published, the art of mathematical typesetting, like that of architectural stonecutting, had died: he could not find a typesetter equal to the task. So he set to work on a computer program for mathematical typesetting and a set of harmonious fonts suitable for computer downloading to a laser printer. The work was done on a PDP-10 at Stanford, running their homegrown operating system WAITS ("It waits on you hand and foot"), in the Sail language. The result, a system called TEX (tau epsilon chi) and METAFONT, its companion font-builder, attracted many devotees, and the original Sail program was soon translated into other languages for portability. It now runs on many different platforms, and is responsible for the production of numerous books and articles of surpassing typographical beauty.

Both TeX and Scribe support a wide variety of output devices, and are among the earliest text formatters to do so. When Xerox let a few of its XGP printers (an experimental Xerographic printer with fonts downloaded from the host) escape into laboratories at Stanford, MIT, and CMU in the early 70's, these were quickly hooked up to PDP-10s, to be driven by formatters like R and Pub. Their flexibility supplied the impetus to people like Don and Brian to include fullblown typesetting concepts in their designs, and because of this, it was possible later to add support to TeX and Scribe for printers like the GSI CAT-4 (then widely used at Bell Labs with Troff), the Xerox Dover, the Imagen, and today's PostScript printers (and if we're not mistaken, Brian was the guiding force behind PostScript too).

In the new millenium, Scribe has pretty much disappeared, which is a shame. But in a way it lives on in LaTEX, which is a Scribe-like language built on top of TEX. Like many tools of the 1970s and 80s, Scribe, TEX, and LaTEX (and, for that matter, EMACS) take a fair amount of study to get started, but it's worth it because once you are comfortable in them, you can out-produce everybody!

Electronic Mail

The benefits of electronic mail hardly need touting, but there was a time when people didn't use it or trust it. Today, many of these same people can scarcely live without it. Its major benefit is that it lets the people who participate in it communicate conveniently, and with some assurance that the message will be received. Unlike postal mail, e-mail can be sent on the spur of the moment and a single message can be sent to more than one person at once. Unlike telephone calls, e-mail does not depend on the callee being present when the message is sent. There are those who say that it's a dehumanizing influence, that people in adjacent offices who once would visit and chat now sit glued to their screens and fire off e-mail messages to each other, messages whose true intent cannot be gleaned from facial expression, body language, or tone of voice. This may be true, but e-mail is here to stay and most people will find a way to fit it into their lives in a sensible way.

Although e-mail had been available for use within a computer since the early 1960s (e.g. on MIT's CTSS timesharing system), e-mail between computers got its start on DEC-20s (or, strictly speaking, KL-10s running TENEX, the "proto-TOPS-20"), at BBN in Cambridge, Massachusetts, in 1972 when Ray Tomlinson of BBN adapted his TENEX e-mail program to send messages to other ARPANET nodes. This involved not just new software and protocols, but also new notation: the now-ubiquitous user@host address format.

If you did a SYSTAT on any DEC-20 at Columbia between 1978 and 1988, you would see about half the users running EMACS and the other half MM, with only occasional time out for text formatting, program compilation, file transfer, and other kinds of "real work". MM is the Mail Manager, originally written by Mike McMahon and taken over later by Mark Crispin. It is the "user agent" side of the mail system. MM is an ordinary unprivileged user program which lets you read your mail, compose and send mail to other users, forward mail, and manage your mail file. MM lets you move messages to different files, to print messages, delete them, flag them for later attention, and so on.

Any operation that MM can perform on a single message can also apply to a message sequence. This is one of MM's most powerful features. MM's message selection functions let you treat your mail file almost like a database, and issue complex queries like "show me (or reply to, or delete, or forward, or flag, or print) all the messages from so-and-so sent between such-and-such dates that are longer than so-many characters and include the word 'foo' in their subject."

MM is enormously powerful, but it's also easy to use because it fully employs the COMND JSYS. Users can find out what's expected at any point by typing a question mark (except when composing message text, in which case the question mark becomes part of the text). There is a SET command that allows many of MM's operations to be customized, and its default actions changed. Users can save these customizations in an initialization file, so they are made automatically every time MM is run.

MM was quickly adopted in favor of DEC-20 MAIL and RDMAIL, and was used initially among the programming staff. Its use quickly spread to the students and faculty, to the extent that several courses came to totally depend on it. Homeworks and readings were assigned, conferences were conducted, assignments turned in, questions asked and answered, all with MM. MM is also used to post messages to public "bulletin boards," which were used for everything from selling used motorcycles to trivia quizzes to raging controversies on political topics.

At Columbia, many of the departments are spread across different buildings, on and off campus. These departments were ideal candidates for electronic mail, and many of them ran their daily business using MM. And MM is equally at home in the networked environment. Given the appropriate network connections and delivery agent, MM can be — and is — used to transmit electronic mail all over the world, faster than any post office or delivery service could deliver paper. From Columbia, we send e-mail to locations as far-flung as Utah, England, Norway, Australia, Brazil, Japan, China, and the USSR, and receive replies within minutes (assuming our correspondents keep the same kind of odd hours we do!).

May 2003 Postscript: It only took another decade for e-mail to become more of a curse than a blessing, and every computer user to be overwhelmed by junk and/or malicious e-mail, known as "spam". The DEC-20 was a pioneer in this area too: the very first spam was sent on 1 May 1978 1233-EDT from DEC-MARLBORO.ARPA (a DEC-20) to all ARPANET contacts (from the WHOIS database), advertising new DEC-20 models.

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OTHER NOTEWORTHY CONTRIBUTIONS

The DEC-20 architecture actually goes back to the mid 1960s, to DEC's PDP-6, which was designed with LISP in mind — the halfwords and associated instructions are perfect for CARs and CDRs (that's LISP talk, descended from instruction set of the IBM 704, where LISP was first developed). Most of the large implementations of LISP were done for DEC's 36-bit machines — MACLISP, INTERLISP — and among the applications based on them, MIT's MACSYMA stands out as a landmark. MACSYMA is used by scientists and engineers to manipulate mathematical expressions of arbitrary complexity on the symbolic, rather than numerical, level. There is one famous (perhaps apocryphal) story about a 19th-century astronomer-mathematician who devoted his life to formulating the exact equation of motion of the moon. The result filled a 300-page book. MACSYMA was given the same problem and solved it in about half an hour, finding a few mistakes in the original to boot.

In 1971, Ralph Gorin of Stanford University wrote the first known computer-based spelling checker for text, SPELL for TOPS-10. It was later adapted to the DEC-20, and "interfaced" with packages like EMACS and MM. The descendents of SPELL are legion — no self-respecting PC-based word processing program would appear in public without a spelling corrector.

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CONVERTING TO UNIX

[Remember: this document was written in 1988.]

"Smooth sailing through the 80's..."(9) By the late '80s, demand for DEC-20 service leveled off and then began to drop. The DEC-20 was like a clipper ship, the highest expression of a technology which many believed obsolete — the large central timesharing computer. Students were now willing to forego the amenities of the DEC-20 for the control and predictability of a PC of their own. Thanks to Columbia's membership in the Apple University Consortium, there were soon thousands of Macintoshes in student hands. Special arrangements with IBM also put IBM PCs in hundreds of offices and dorm rooms. These systems met student's needs for small programming assignments in Pascal and Basic, as well as for modest word processing, and relieved the central systems of a large burden. However, PCs did not fulfill the needs of the Computer Science and other engineering departments, where larger projects were assigned in languages like Fortran, C, Prolog, and Lisp, which were not readily and affordably available for PCs.

Meanwhile, UNIX was taking over the computing world — on mainframes, minis, workstations, and even PCs. Our major group of instructional users — CS students — were doing most of their work on departmental ATT 3B2's, but badly needed a centralized, reliable environment with tolerable performance, backups, service, and all the rest. We already had been running UNIX on a VAX 750 for some years (for internal development work), as well as Amdahl UTS on an IBM mainframe, so had developed some UNIX expertise.

For these reasons, we decided that it was time to start converting from TOPS-20 to UNIX. For financial reasons, we chose a VAX 8650 for this purpose. The DEC-20 tradein was attractive, and we were able to keep our old disk and tape drives. In fact, we figured that over 3 years, buying the VAX was cheaper than keeping the DEC-20. And it was more powerful, with a bigger address space, in a smaller footprint, than the DEC-20 it replaced.

VMS was not chosen for several reasons. First, we were feeling somewhat betrayed by DEC's abandonment of TOPS-20, and did not want to leave ourselves open to the same treatment in the future. UNIX, unlike VMS, does not tie you to a particular vendor. Furthermore, UNIX has networking and communications for all our major requirements: Ethernet, TCP/IP, DECnet (our initial UNIX was Ultrix-32), BITNET (UREP), RS-232 and LAT terminals, Kermit. And UNIX itself has many benefits: a very powerful applications development environment for experienced programmers, a programmable shell, piping of programs, simple but powerful utilities.

UNIX, however, is notoriously terse, cryptic and unfriendly, especially to novice computer users. VMS, though lacking the DEC-20's COMND JSYS, is certainly friendlier than UNIX, and verbose to a fault. So it was not without some misgivings that we embarked on the conversion.

Many of us DEC-20 users were resistant to change. Familiarity, for better or for worse, is often more appealing than uncertainty. But converting to UNIX did force us to give up some of the features which originally drew us to the DEC-20 in the first place.

The "user-friendly" shell provided by the TOPS-20 Exec, which gives help to those who need it but does not penalize expert users, is probably the feature that was missed the most. In UNIX, most commands are programs, assumed to have arguments of only options or filenames. This means you can't have "?" for commands and arguments in the shell, because the programs that would act upon the help request hasn't even started running yet. This is the opposite of TOPS-20, where most major functions are built into the exec, but which doesn't allow concise building-block programs to be piped together as UNIX does.

To cite an example of the radical difference between the TOPS-20 and UNIX philosophies, suppose you wanted to create a procedure that would produce a directory listing, sort it in reverse order by filesize, and format the listing into numbered pages with three columns per page, suitable for printing. In TOPS-20 you would spend a week writing an assembly language program to do all of this. In UNIX, the tools are already there and only need to be combined in the desired way:

  ls -s | sort -r | pr -3

This makes UNIX look pretty attractive. But the DEC-20 program, once written, will contain built-in help, command and filename completion, etc, whereas the UNIX procedure can only be used by those who know exactly what they are doing. If you've typed "ls -s | sort" but don't know what the appropriate sort option is, typing question mark at that point won't do any good because the sort program isn't running yet.

The DEC-20 (like most common operating systems) uses case-independent commands and filenames. Case dependence, however, is a feature of UNIX which is vigorously defended by its advocates. It can be quite confusing to users of other operating systems. In general, UNIX commands are very different from the commands used in other systems. Even if the DEC-20 had not offered a menu-on-demand help facility the average user could have probably guessed the proper commands to type — DELETE to delete a file, COPY to copy a file, RENAME to rename a file, etc. In UNIX, how do you delete a file? DELETE? No.... ERASE? No, it's "rm" (small letters only!).

Without a manual at your side, how could you find this out? Even if you knew about "man -k" (keyword search through the online manual), UNIX doesn't give you much assistance: "man -k delete" doesn't turn up anything relevant, neither does "man -k erase". But at least "rm" is somewhat suggestive of the word "remove", and indeed "man -k remove" would have uncovered the elusive command (early versions of UNIX had an even more elusive name for this command: dsw, an abbreviation for "do swedanya", Russian for goodbye, transliterated into Polish or perhaps German; this is not the only place where the censor has been at work... Current "standard" versions of UNIX do not have a "help" command, but in earlier releases, a help command was provided which declared simply, "UNIX helps those who help themselves").

I (fdc) can't remember where I dug up the "do swedanya" reference, but evidently it's an urban legend. Dennis Ritchie said in a 1981 Usenet posting that the actual etymology is "delete from switches"; the original PDP-7 dsw program was a precursor to "rm -i" (remove interactively), in which the CPU switches provided the interaction.

A special amenity of TOPS-20 is its retention of multiple generations (versions) of each file, giving the ability to revert to an earlier version should the latest one suffer from human error, folly, or tragedy. This, coupled with the ability to resurrect a file after it is deleted, imparts a sense of comfort and security that can only be appreciated once one moves to a more conventional and precarious file system. If you delete a file in UNIX, or create a new file with the same name as an existing one, then the old file is just plain gone. The "rm *" command in UNIX is simply too powerful, and too silent. Yes, it did what you said, but how did it know you meant what you said? UNIX does not save users from themselves. After accidentally deleting all your files in UNIX you will never again be annoyed when you type a command and it asks "Are you sure?".

Another important feature of TOPS-20 is the logical device name, which can be defined in infinite variety for the system as a whole, and for each individual user. Each logical name can point to a particular device and/or directory, or to a whole series of them, to be searched in order. These are built into the operating system itself, whereas the notion of PATH and CDPATH are afterthoughts, grafted into the UNIX shell, not available from within programs, and not applicable outside their limited spheres of operation.

Then we have the programming languages which would no longer be available — ALGOL (60 & 68), APL, BASIC, BCPL, BLISS (10, 11, and 36), CPL (and "real" PL/I), ECL, FOCAL, PPL, SAIL, SIMULA, SNOBOL, ... And TECO! And MACRO and Midas and Fail... In fact, few people will miss any of these, with the possible exceptions of APL (used in some classes) and SNOBOL (which can still be found for UNIX on selected platforms).

Of course all our homegrown applications written in assembly language had to be be redone for UNIX: user ID entry and management (as opposed to editing the passwd file), accounting, user restrictions (ACJ, Omega). And one feature which we could never again live without is MM, a powerful mail management system equally usable by novices and experts.

On the positive side, we would not be giving up EMACS, Scribe, TeX, Kermit, or the TCP/IP utilities Telnet and FTP. All of these programs are available in some form for UNIX. Some of the UNIX implementations are definite improvements, such as GNU EMACS from the Free Software Foundation, without the memory limitations of TOPS-20 EMACS. There is also a high quality Fortran from DEC for our engineers, and of course the whole C and LISP programming environments for CS students and other software developers, plus a set of powerful text manipulation utilities like sed, grep, awk, lex, and yacc, whose functions should be obvious from their names.

The VAX installation was much quicker than the typical DEC-20 installation. The 8650's performance was quite snappy, and its reliability was excellent. After one year, the 8650 was sold, and a second DEC-2065 was traded in to DEC for a VAX 8700. The 8700 is about the same power as the 8650, but, unlike the 8650, is compatible with the new BI devices, and upgradable to a bigger model VAX should it run out of steam.

It turned out, however, that it when it came time for expansion, it was more cost-effective to buy Sun UNIX systems rather than upgrade the 8700 to a bigger VAX. This is a choice you don't get with a proprietary operating system like TOPS-20, VMS, etc. Converting from a VAX to a SUN requires some "giving up" (e.g. DECnet) but not nearly so much as the journey from DEC-20 to VAX, and in return you get a very powerful machine in a fraction of the VAX's floorspace — what the Jupiter should have been, but with UNIX instead of TOPS-20.

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MAJOR CONVERSION ISSUES

[Remember: this was written in 1988.]

A big question during the conversion to UNIX was user education. UNIX does not help users the way TOPS-20 does. There is no COMND-style ? help, there is not even a "help" command. The commands themselves do not have intuitive names: a user would be hard-pressed to guess that "mv" is the command to rename a file, "cat" to type a file, etc. How will users know how to respond to the mute "$" (or "%") staring them in the face? Should we write a user-friendly shell for them? Or reams of tutorials and reference manuals?

For all its cryptic terseness, UNIX has become very popular. UNIX systems run on computers of all kinds, from PCs to supercomputers. Consequently, computer bookstores are loaded with books of the "Teach Yourself UNIX" variety. Our feeling has been that no matter how cryptic and unfriendly UNIX itself may be, it shouldn't be changed. Otherwise we lose the compatibility with other UNIX systems, the books and articles, we leave ourselves open to a maintenance nightmare, and we let our users in for a rude surprise should they ever encounter a real UNIX system.

Another issue is the mail system. As the user-level mail agent, you have the choice of UNIX mail or GNU EMACS RMAIL. UNIX mail is primitive and unintuitive, and RMAIL is accessible only to those who know EMACS. RMAIL has the advantage of a consistent interface — no jumping in and out of the editor — but it has a relatively limited command repertoire.

Our users have become very much acclimated to electronic mail, thanks largely to the power, convenience, and friendliness of MM. Many of the biggest users of MM are faculty or administrators who do not need to learn a new mail system. But a program as powerful as MM requires a lot of commands, and when you have many commands, you need the kind of built-in help that comes for free on the DEC-20. Similar comments apply to other complicated programs, for example (on our system) user ID entry and management programs, the operator interface (like OPR on the DEC-20), etc.

For this reason, we decided to "turn our new system into our beloved old one" by writing a COMND package for UNIX. This package, CCMD, started as part of the "Hermit" project, a Columbia research effort funded by DEC, 1983-87. We were trying to design a network architecture that would allow various kinds of PCs — IBM, Rainbow, Pro-380, VAXstation, SUN, Macintosh, etc — access to the files and services of our DEC-20 and IBM mainframes in a consistent and transparent way. The project ultimately failed, because technology passed us by (cheap Ethernet & token ring connections and gateways, Sun NFS, VAX-based Macintosh file servers, etc).

CCMD, written entirely in C, does all COMND functions and more, parses from the terminal, a file, redirected standard input, or a string in memory. It's not oriented to any specific keyboard or screen. It favors neither the novice nor the expert. It runs under 4.xBSD, Ultrix, AT&T System V, SunOS, and MS-DOS, and it should be easily portable to VAX/VMS, and any other system with a C compiler.

CCMD is a fullblown COMND implementation, allowing chained FDBs (e.g. parse a filename, or a number, or a date), redirection of command input, and so forth. Additions to the DEC-20 COMND JSYS include "?"-help lists for matching filenames, partial filename completion (up to first character that's not unique), a very flexible time and date parser, and additional data types.

Using CCMD, Columbia's programmers were able to write a clone of DEC-20 MM entirely in C. It has all the features of DEC-20 MM, plus a few more. It handles a variety of mail-file formats, including DEC-20, Babyl (RMAIL), and mbox (UNIX mail). It uses UNIX sendmail as its delivery system, and should be adaptable to the delivery services of non-UNIX systems.

The authors — and a surprising number of other people all over the world — still use Columbia MM today as their mail client. It can be built and installed on (at least) Linux, FreeBSD, OpenBSD, NetBSD, Solaris, and SunOS. You can find it HERE

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FINAL WORDS...

[Remember: this was written in 1988.]

Columbia is highly decentralized and facing the budget squeeze common to all higher education institutions. There is no central mandate to put expensive workstations on every desk, connected by gigabit fiber optic networks. Students, faculty, and staff for the most part use their own or departmental funds to get the best PC they can use, typically an IBM PC or Macintosh with an RS-232 interface. Most users communicate only sporadically via dialup, or by hauling a diskette to a public PC lab, where PCs are connected to the network or a laser printer.

As PCs become cheaper and more powerful, what's left to be done centrally? There are those who claim that anything a VAX or DEC-20 can do, can also be done on a PC. The only exceptions might be very large applications, shared and/or large and/or constantly changing databases, and communication in general — wide area networks, mail, shared program libraries, bulletin boards, conferences, ...

But massive decentralization of computing means enormous duplication of effort and expense for hardware, software licenses, and maintenance. Everyone becomes a system manager, doing backups, troubleshooting, software installation and debugging, consulting, training, scrounging for parts. Researchers who were once hot on the trail of a cure for cancer or AIDS are now twiddling DIP switches, running Norton utilities on their fractured hard disks, poring through the back pages of BYTE for bargains. Each person or group may have a unique collection of software & hardware, which makes instruction, collaboration, and most other functions much more difficult than in the timesharing days. And space must be found for computing equipment in practically every office and dorm room, rather than in one central area. Some day, the budgeteers might notice the cumulative effect of all this distributed computing and the pendulum will start to swing back the other way. What's the phrase, "economies of scale?"...

There was an article in the paper some years ago during the fuel crisis, about bringing back clipper ships... The DEC large systems, the clipper ships of the timesharing era, will never return, but they will live on in the software they spawned — EMACS, TeX, Scribe, Spell, MM, Kermit, advanced LISP dialects, and so on. Meanwhile, as the computer industry struggles to turn PCs into multiuser systems and to reinvent multiprocessing, security, and other forgotten concepts, it might profitably pause to look back at the past decades, when the expense and limitations of computing equipment forced designers and coders to be... well, smarter.

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EPILOG

(January 2001)

Today, when you can walk into an ordinary retail store and buy a computer with 10 times the power (and 100 times the main memory, and 1000 times the disk capacity) of the biggest, fastest KL10 ever made for under $1000, plug it into an ordinary wall socket and phone jack (or cable box, etc), and be on the Internet in a few minutes with full-color graphics, video, sound, and who knows what else, we might easily forget how computers have evolved from big standalone stored-program calculators into "communicators". At least for us at Columbia University, the change began with the large DEC systems that exposed us all at once to file sharing, electronic mail, and local and wide-area networking, opening up possibilities of collaboration and communication in work and in life: within the computer, across the campus, and around the world.

The PDP-10 postmortem has been long and painful (who killed it and why, how might it have survived, and what would the world be like today if it had), but those who might still like a glimpse into the exciting times of 1970s and 80s when computers first became a cultural phenomenon and a communication medium can now do so with several software-based PDP-10 emulation projects underway. Perhaps the greatest legacy of those days is found in today's open software movement, in which developers all over the world cooperate on projects ranging from operating systems (Linux, FreeBSD, etc) to applications of all kinds, just like the original PDP-10 ARPANET "hackers" did (whether this is a viable business model is a separate question :-)

Meanwhile, many of us who lived through that era retain our old habits, still using text-based applications such as EMACS and MM (or its successor, Pine) rather than their fashionable GUI replacements, but on UNIX platforms (Solaris, Linux, etc) instead of PDP-10s. Each time a new PC virus plunges the entire planet into chaos and panic, we barely notice. There is something to be said for the old ways.

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GLOSSARY

3270     IBM System/370 fullscreen blockmode terminal
ACJ      Access Control Job (TOPS-20)
AOS      Add One and Skip (PDP-10 instruction)
APL      A (cryptic) Programming Language, Kenneth E. Iverson (1966)
ARPANET  (US Defense Department) Advanced Research Projects Agency Network, which became the worldwide Internet.
ASP      Attached Support Processor (IBM 360 terminal monitor)
BALR     Branch and Link Register (IBM 360 instruction)
BASIC    Basic All Purpose Symbolic Instruction Code
BBN      Bolt Beranek and Newman, developers of TENEX and much of ARPANET
BITNET   Because-It's-There Network (based on IBM remote job entry)
BLT      Block Transfer (PDP-10 instruction)
CACM     Communications of the Association for Computing Machiner (journal)
CCMD     COMND JSYS package written in C
CCNET    Computer Center Network (based on DECnet)
CFS      Common File System (TOPS-20)
COMND    The Command JSYS mnemonic (TOPS-20).
CP/M     Control Program / Microcomputer (early OS for 8-bit PCs)
CPU      Central Processing Unit
CTSS     MIT's Compatible Time Sharing System for the IBM 7094
CU20B    Columbia University's 2nd and longest-lived DEC-20
DDT      Dynamic Debugging Tool (PDP-10) Originally DEC Debugging Tape (PDP-1)
DEC      Digital Equipment Corporation, 1957-1998 (purchased in 1998 by Compaq, purchased in turn by HP in 2001)
DEC-20   The DECSYSTEM-20, a PDP-10 specially designed to run TOPS-20
DECNET   DEC's proprietary networking suite for most of its OS's
DN20     A full-cabinet PDP-11/34 communications front end for the DEC-20
DN200    A full-cabinet PDP-11/34 terminal/printer concentrator for the DEC-20
DOLPHIN  A never-completed followon to the KL10
EMACS    Editing Macros: Richard Stallman's fullscreen editor originally based on TECO
ESC      The Escape (Altmode) control character (ASCII 27)
FAIL     Ralph Gorin's fast PDP-10 assembler
FORTRAN  Formula Translator: the first high-level programming language (1957)
FTP      File Transfer Protocol (ARPANET/Internet)
HASP     Houston Automatic Spooling Program
HRROI    Half Right to Right Ones Immediate (PDP-10 instruction)
IEEE     Institute of Electrical and Electronics Engineers
ILDB     Increment Pointer and Load Byte (PDP-10 instruction)
ITS      Incompatible Timesharing System (for PDP-10 at MIT; pun on CTSS (q.v.))
JCL      Job Control Language (IBM OS/360)
JRST     Jump and Restore (PDP-10 instruction)
JSYS     Jump to System (PDP-10 instruction)
JUPITER  Another never-completed followon to the KL10
JVNCNET  John Von Neumann Supercomputer Center Network (Princeton)
KA10     First PDP-10 model, only runs TOPS-10
KI10     Second PDP-10 model, only runs TOPS-10
KL10     Third and biggest / most advanced PDP-10 model, runs TOPS-10 and -20
KS10     Fourth, small PDP-10 model, runs TOPS-10 and -20
LCG      DEC's Large Computer Group, responsible for PDP-10s
LISP     List Processing Language (Jon McCarthy, Stanford U, 1960)
MACRO    DEC's family of assemblers: MACRO-10, MACRO-11, MACRO-20, etc
MIDAS    MIT's PDP-10 assembler
MINNOW   A desktop PDP-10 (never completed)
MIT      Massachusetts Institute of Technology
MM       Mail Manager (a DEC-20 — and later UNIX — e-mail client)
MS-DOS   Microsoft Disk Operating System
NCP      Network Control Program (early ARPANET protocol replaced by TCP/IP)
NJE      Network Job Entry
NYSERNET New York State Engineering and Research Network
PARC     Xerox Palo Alto Research Center
PBX      Private Branch Exchange
PDP      Programmed Data Processor (PDP-7, PDP-8, PDP-10, PDP-11, others)
RA81     A later-model, bigger, sealed disk (but still washing-machine size)
RAID     Ralph Gorin's PDP-10 debugger
RJE      Remote Job Entry (card reader / line printer simulation)
RP04     The most common PDP-10 disk drive in the mid-to-late 1970s
RP06     The most common PDP-10 disk drive in the late 1970s - early 80s
RSCS     Remote Spooling Communications Subsystem (BITNET protocols)
RSTS/E   DEC's Resource-Sharing Time-Sharing / Extended operating system for the PDP-11
RSX11    DEC's Realtime Executive for the PDP-11 (not an acronym)
RSX20F   A special version of RSX11 for the KL10 front end, which handled all the terminal I/O for the KL10 back end.
SOS      Son Of Stopgap (TOPS-20 line editor)
SSIO     Columbia's Self Service Input/Output Area
TCP/IP   Transmission Control Protocol / Internet Protocol
TECO     Text Editor and Corrector
TENEX    The paged PDP-10 operating system from BBN, precursor to TOPS-20
TOPS-10  The Operating System (PDP-10, DECsystem-10)
TOPS-20  The Operating System (DECSYSTEM-20)
TTY      Teletype or Teletypewriter; that is, a terminal or terminal port
UNIX     Popular operating system originally from Bell Labs (not an acronym)
UREP     The UNIX version of RSCS, allowing UNIXes to participate in BITNET
VAX      Virtual Address Extended, DEC's 32-bit follow-on to the PDP-11
VMS      Virtual Memory System, DEC's operating system for the VAX
VT100    DEC's 24x80 upper/lower-case smooth-scrolling video terminal (1977)
WAITS    Stanford's PDP-10 operating system ("it WAITS on you hand and foot")
XOFF     Control-S (ASCII 19), used for host/terminal flow control
XON      Control-Q (ASCII 17), used for host/terminal flow control

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ACKNOWLEDGEMENTS

[1] Bob Clements, BBN (2001).
[2] Joe Dempster, DEC (1988).
[3] Mark Crispin, University of Washington (2001).

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NOTES

  1. The Computer Museum in Boston is now defunct, as is Digital Equipment Corporation (DEC), its original sponsor. Its collection has moved, hopefully in its entirety, to the Computer Museum History Center in Moffet Field, California:

      http://www.computerhistory.org/
    

    where a search for "360/91" turns up the following:

       Artifact Name: System 360 Model 91 Operator Console
        Manufacturer: International Business Machines Corporation (IBM) 
        Model Number: 360/91 or 91
    	Category: Transducer: control panel
    	    Year: ca 1968
      History Center: ID # X01321.1997
    

    There is no picture, but if memory serves, it was about 4 feet tall and 6 feet wide, with perhaps 16 light bulbs per square inch. The "IBM 360/91" nameplate was stolen while it was waiting for pickup. The rest of the machine was chainsawed and thrown in acid baths to extract the gold.

  2. TECO (Text Editor and Corrector) was both an editor and a language for writing editors. When used "bare" its command language was sparse and cryptic, similar to DDT. When used as a basis for "higher level" products, such as EMACS, its power could readily be appreciated. "Make love, not war!" was a familiar chant at the anti-Vietnam-war demonstrations of the 1960s and 70s.

  3. For those who don't recall, an RP06 is the size of a dishwasher, weighs a ton, and uses a removable disk pack that can hold about 175 Megabytes. In 1977 it was exciting news, as it doubled the the capacity of its predecessor, the RP04.

  4. DDT dates from the PDP-1 (where it stood for DEC Debugging Tape, since it was executed from paper tape), circa 1960, via the PDP-6 (which was the predecessor to the PDP-10), and descends from an earlier bug-killer, FLIT (Flexowriter Interrogation Tape) on the PDP-1's predecessor, the TX-0, on the 2nd floor of MIT building 26. Both DDT and TECO were originally done at MIT for the PDP-1 [1]. DDT lives on in present-day debuggers such as GDB, where most of its concepts — if not its unique user interface — survive.

  5. The steady stream of characters caused a crash; the system recovered but the steady stream continued; the system crashed again, and so on throughout the night.

  6. 8-bit commands are also possible but not required. Originally, they were produced with a "Meta" key, which was available on certain select terminals, like the Datamedia 2500. But since about 1990, it has become more important to be able to enter 8-bit data characters, such as the accented letters of Italian and Spanish; the special letters of German and Icelandic; the non-Roman letters of Russian, Greek, Hebrew, and so on.

  7. Newcomers to computing might not appreciate the separation of text editing from text formatting, or the advantage of embedding plain-text formatting commands in the text over manually making this word bold, that word italic, and so on, in a word processor. But this is not the place to explain it.

  8. Ownership of Scribe has changed hands several times since then and is no longer easily pinned down, but reportedly [2001] they are still in business.

  9. This was LCG's slogan, meant to reassure its customers that the 36-bit line of computers would be viable throughout the 1980s. Cups, T-Shirts, stickers, and other knicknacks bearing this slogan and a sailboat logo were given out in vast quantities around 1980-82.

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BIBLIOGRAPHY

  1. Allen, John, Anatomy of Lisp, McGraw-Hill, ISBN 007001115X, 1978.

  2. Bobrow, D.G., and J.D. Burchfiel, D.L. Murphy, R.S. Tomlinson, TENEX, A Paged Timesharing System for the PDP-10, CACM Vol 15 No 3, March 1972.

  3. da Cruz, Frank, Kermit, A File Transfer Protocol, Digital Press, 1987.

  4. DECsystem-10/DECSYSTEM-20 Hardware Reference Manual, Volume I, Central Processor, Digital Equipment Corporation, EK-10/20-HR-001, 1978.

  5. TOPS-20 Monitor Calls Reference Manual, AA-FV52A-TM (e.g. for TOPS-20 6.1, September 1985).

  6. MACRO Assembler Reference Manual, AA-4159B-TM, April 1977.

  7. DECsystem-10 Journal of Applications and Research (undated; probably 1973 or 1974 and probably the one and only issue); predecessor of the Digital Technical Journal.

  8. Gianone, Christine, Editor, Kermit News, published periodically by the Kermit Project, Columbia University, 612 West 115th Street, New York, NY 10025.

  9. Gorin, Ralph, Introduction to DECSYSTEM-20 Assembly Language Programming, Digital Press, 1981.

  10. Knuth, Donald E, Art of Computer Programming, ...

  11. Knuth, Donald E, TeX and Metafont, Digital Press, 1979 (now a collector's item).

  12. Murphy, Dan, Storage Organization and Management in TENEX, AFIPS Conference Proceedings Vol. 41, 1972.

  13. Peterson, James L., Computer Programs for Detecting and Correcting Spelling Errors, CACM, V23 #12, Dec 1980.

  14. Stallman, Richard M., EMACS, the extensible, customizable, self-documenting display editor, ACM SIGPLAN Notices, V16 #6, June 1981.

  15. Steele, Guy L., Don Woods, Raphael Finkel, Mark Crispin, Geoff Goodfellow, Richard Stallman, The Hacker's Dictionary, Harper & Row, 1983.

  16. Hafner, Katie, and Matthew Lyon, Talking Headers (the history of electronic mail), Washington Post Magazine, August 4, 1996.

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LINKS

(January 2001 - March 2003) Caution: Links go stale faster than anybody can keep up with.

KLH-10: Ken Harrenstein's KL10/KS10 emulator (first released 10 Nov 2001):
http://klh10.trailing-edge.com (ANNOUNCEMENT).

TS10: Tim Stark's PDP-10 emulator (First released 7 March 2001):
ftp://ftp.firesword7.net/pub/ts10/stable/ (FTP)
http://www.sourceforge.net/projects/ts10/stable/ (CVS)

Bob Supnik's SIMH PDP-1/4/7/8/9/10/11/15 emulator:
http://simh.trailing-edge.com/

Miscellaneous PDP-10 emulators in various stages of development (Zane Healy):
http://www.aracnet.com/~healyzh/pdp10emu.html

Paul Allen's PDP Planet (PDP-10, PDP-11, PDP-8 restoration and preservation project)
http://www.pdpplanet.com

Introduction to using the DECSYSTEM-20 (Dundee Tech)
http://www.36bit.org/dec/third_party_doc/dundee_pi16.txt

The History of Computing at Columbia University:
http://www.columbia.edu/cu/computinghistory/

DECSYSTEM-20 Programming Languages (Columbia U):
http://pdp-10.trailing-edge.com/mit_emacs_170_teco_1220/01/info/old-languages.info.html
ftp://kermit.columbia.edu/kermit/dec20/languages.info

DECSYSTEM 20 Assembly Language Programming Guide (Columbia U):
ftp://kermit.columbia.edu/kermit/dec20/assembler-guide.txt

The Kermit Project Website:
http://www.columbia.edu/kermit/

DECsystem-10 Kermit:
The PDP-10 Kermit webpage

DECSYSTEM-20 Kermit:
The PDP-10 Kermit webpage

MM and CCMD:
DOWNLOAD, Documentation.

The Free Software Foundation (it started with EMACS on a PDP-10):
http://www.gnu.org/

The Computer Museum History Center:
http://www.computerhistory.org/

Dan Murphy's Origins and Development of TOPS-20:
http://ns.opost.com/dlm/tenex/hbook.html

Dan Murphy's TENEX and TOPS-20 Papers:
http://www.opost.com/dlm/tenex/index.html

Les Earnest: SAIL Away
http://www.stanford.edu/~learnest/sailaway.htm

ITS - The Incompatible Timesharing System
http://www.cosmic.com/u/mirian/its/

John McCarthy's History Pages:
http://www-formal.stanford.edu/jmc/history/

Unix for TOPS-20 Users by Nelson Beebe
http://www.math.utah.edu/~beebe/publications/1987/t20unix.pdf

PDP-10 Webring:
http://n.webring.com/hub?ring=pdp10&id=1&hub

Gordon Bell's CyberMuseum for Digital Equipment Corporation:
http://research.microsoft.com/~gbell/Digital/DECMuseum.htm

Digital Computing Timeline:
http://www.montagar.com/dfwcug/VMS_HTML/timeline/tmlnhome.htm

Tim Shoppa's PDP-10 Software Archive:
http://pdp-10.trailing-edge.com/

Joe Smith's 36 bits forever!:
http://www.inwap.com/pdp10/

Tymshare PDP-10 (KA, KI, KL) photos from 1980:
http://www.inwap.com/pdp10/tymshare/BubbRoad/

SDF Public Access TWENEX::
http://twenex.org

GCC for the PDP-10:
http://pdp10.nocrew.org/gcc/

NetBSD for the PDP-10:
http://www.netbsd.org/Ports/pdp10/

Additional Glossary (primarily for RJE/NJE terms and acronyms):
http://publib.boulder.ibm.com/cgi-bin/bookmgr/BOOKS/IEA1M503/GLOSSARY

The PDP-10 newsgroup:
news:alt.sys.pdp10

The Kermit newsgroup:
news:comp.protocols.kermit.misc
Archives (1994-present)

The Info-Kermit Digest
Info-Kermit Digest Archives (1983-1995)

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DECSYSTEM-20 at Columbia University / fdc@columbia.edu / Dec 1988 - Aug 2008