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A Brief History of 36-bit Computing at CompuServe

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File name:  COMPUS.TXT 
Date:  31-Aug-88 15:44 EDT
From:  Sandy Trevor [70000,130]
Subj:  PDP-10 History

TO: Joe Dempster

This may not be exactly what you had in mind, but it is a pretty accurate
summary of how 10's have been used at CompuServe over the past 17 years.
I hope you can use it... anyway, please do keep me updated on your
project. (If you want changes, or more material, just let me know).
Also, if you do decide you want to use this, I'd like a chance to edit
it a bit before giving you a "final" version.  So please consider this
a prelimary version...


			  We Call Them 10's

	- A Brief History of 36-bit Computing at CompuServe -

			 Alexander B. Trevor
			   August 31, 1988

    CompuServe has one of the world's most powerful remaining
thirty-six bit computing facilities, but got its first PDP-10 almost
by accident.  While I was a graduate student at the University of
Arizona's Analog Hybrid Computer Lab (AHCL) in 1969, I discussed with
two other students the idea of starting a time-sharing company after
completing our degrees.  We had all gotten to know a PDP-15
intimately at AHCL, so it was the obvious cpu of choice.  But my
choices in late 1969 were the Army or Canada.  I chose the former,
which put me behind a 360-40 in Saigon instead of a PDP-15 in Tucson.
Meanwhile, my two AHCL friends, Dr. John Goltz and Jeff Wilkins, went
to Columbus, Ohio, where they intended to computerize insurance
processing for Golden United Life Insurance with (of course) a
PDP-15.  Before the 15 was delivered, however, DEC called up Dr. Goltz
and told him that for only "a little more" he could have a KA-10.  The
prospect of having all this power was irresistible.  Though he liked
to distance himself from those of the sales persuasion, John
skillfully sold the board of directors on the idea of spending the
extra money to buy the PDP-10 and thereby gain the excess computer
power to be able to launch into timesharing.
    Of course, it was a terrible time to get into this business. GE,
Tymshare, Cyphernetics, and First Data (to name just a few) were
already well established.  The timesharing subsidiary of Golden United
took the name "CompuServ Network, Incorporated" and started
developing its first application, LIDIS (Life Insurance Data
Information System).  They had a KA-10 with all of 80K words of 
memory, two RP02 disk drives, and a few ASR-33 teletypes.
The "C" series of TOPS-10 monitors that was available in 1970
supported disks, but as little more than circular DECtapes.  Still,
CompuServ made LIDIS work, and began attracting other clients.
    From the beginning, CompuServ tried to improve upon the standard
DEC offerings. A first step was to hire two of the engineers who
installed the machine: Bill Spellman and Tom Shelton. Tom would look
at the the lights of an ailing KA for a minute or two (KA's had MANY
lights), then go in back and change one or two boards. Usually, he
fixed the machine on the first try this way, notwithstanding having
been hauled out of bed at 3 a.m.
    A second step was to improve TOPS-10. At that time DEC included
operating system sources with every machine. You needed them too: the
early releases of TOPS-10 did not terminate a job if someone hung up
without logging off. Thus, the next person calling in on that line
found himself in the previous user's job, with access to all his
files and privileges -- the infamous ghost port.  Needless to say,
customers got pretty upset when this occurred, so we fixed it quickly.
    Some monitor hazards took longer to surface.  One morning, when
the engineers looked at the KA, strange patterns were dancing across
the console lights.  Spellman was about to shut down the machine,
when Steve Wilhite grabbed him and told him it was "just a little
program I wrote."  The next day, the LIGHTS UUO (CALLI -1) was
    Another motivation for modifying the operating system came with
the first release of the "D" series monitor -- the first one with a
real file system, including the beloved MFD, UFD's, RIB's, and SAT's.
The first "D" monitor did not work for more than a hour at a time.
John Goltz stayed up for three days patching the "D" monitor well
enough so that calls from our customers no longer included threats of
bodily injury.
    I seem to walk into things right after the fun. I went to Vietnam
right after the great Tet Offensive of 1968. I joined CompuServe in
1971, right after the "D" monitor crisis. (It is still unclear to me
which of these two events will turn out to be the most significant.)
In any case, when I joined CompuServe in late 1971, they had two
KA-10's, each with four RP02's.
    My first task was to write UNSPOL (DEC's spooling software was
not yet available).  Our machines were getting bogged down with jobs
running "GLOM" - a little routine that continually tried to assign
the line printer.  We wrote most of our own utilities, either because
we wanted features not yet available then from DEC, or because the
DEC equivalents were not compatible with our monitor, which was
rapidly diverging from standard TOPS-10. Or maybe we just liked to be
different.  Early on John had written a new EXECUTE that used sixbit
command files instead of the DEC standard ASCII (to save disk space).
Of course, this required changing all CUSPS (Commonly Used System
ProgramS) and compilers.  (Back then, programmers were cheaper than
   The monitor's command decoder was another area of great change. We
perceived GE as our prime competition, so many things were done to
make former GE clients feel at home -- including the "OK" prompt, an
imbedded line numbered editor in the monitor, and having Steve
Wilhite write a Basic compiler in Macro-10 from scratch. At that
point we didn't know that a compiler was too big a job for one
programmer, and fortunately neither did Steve.  Emerging from the
dark back room we called the "cave" only to grab a line printer
listing or an occasional sandwich, he got it done in ten months,
using an ASR-33 and our FILGE editor.  Everyone loved his Basic, but
I'm not sure how many customers really switched from GE because of
   During this period we learned to get the most out of the KA --
doing things such as using MOVEI A,N(A) for addition because address
arithmetic was faster than the regular adder on the KA.
   CompuServ's two KA-10's were each connected to 680i front-ends
through DA-10 interfaces. The 680i was a PDP-8 that had been
lobotomized to handle communications. UART chips were not yet in
common use, so the 680i's had to handle asynchronous characters one
bit at a time.  One disadvantage of this configuration was that
communications ports were tied to a single host KA. For example, the
remote lines from Dayton and Cleveland were connected to System 1,
while Columbus and Detroit were on System 2. So what did you do with
a customer with offices in all four cities?  My second major
assignment at CompuServ was to solve this problem.
    Clearly, some kind of switch was needed so that a user coming in
through either 680i could access either host. And what was Dr.
Goltz's choice for the switching computer?  Right, a PDP-15. It was
an 18 bit machine (exactly half the PDP-10 word length), fast (1
MIP), and fortuitously, compatible with the DA-10. Now, this PDP-15
that I had to develop into an intelligent communications switch came
with 8K of memory and an KSR-35. That was it -- no mass storage, not
even a Dectape. Since I did not relish doing development on paper
tape, I decided I had to use the 10 for development. Since there was
no cross assembler for the PDP-15, I wrote macros for each of the
PDP-15 instructions and used Macro-10 to generate PDP-15 object
code... a use that probably even exceeded the wildest fantasies of
Macro-10's developers.
    In 1973 CompuServ moved to a new custom building in Upper
Arlington, Ohio, and upgraded the KA's to KI's. By July, 1974, we had
seven KI's and were using them not only to support a thriving time
sharing business, but also to heat our office buildings.  The RP02'S
and RP03's were all retired in favor of "huge" 200mb Ampex and Memorex
3330 disks connected through Systems Concepts SA-10's.  John Goltz
continued to develop his operating system (now called the "E"
monitor), including a class scheduler.
    But by 1976 a more pressing problem arose.  DEC had released the
KL-10, but it seemed prone to overheating (ECL does generate a lot of
heat). Dr. Goltz felt we needed a faster processor, but the KL was
unsuitable.  We looked at Foonly's F1, but were uneasy about their
ability to actually produce machines.  So, with two of our best
engineers, Doug Chinnock and Wilson Mowbray, John Goltz set up an R&D
center in Tucson, Arizona, to build a better 36-bit computer.  In 18
months, they had several large boards, microcode that avoided all the
DEC patents, but were still a good year from having a production
machine.  Jeff Wilkins was running short on enthusiasm (and cash) for
the project, and it looked like DEC had really solved the KL-10 heat
problem with the DEC-System 20 configuration. Not only that, but the
price of the 2050 was at least $100K lower than the 1090.  Internal
memory and devices on RH-20's seemed not only more efficient, but
saved us from having to add cache sweeps to our monitor. If we could
run our operating system on this machine, it might make more sense
than finishing the "JRG-1" processor.
    After several trips to Marlborough, I got DEC to agree to sell us
DECSYSTEM-20's with TOPS-10 licenses and DX-20's. The licenses
eliminated any question about running any of the TOPS-10 utilities,
and the DX-20's let us connect the orange KL-10's to our STC tape
pool. Our first 2050 worked beautifully, so the JRG-1 project was
terminated. Sadly, not long afterwards, Dr. Goltz left CompuServe.
    We had been buying Ampex's ARM-10 memory for the KI's for years,
so we asked them what they could do for the 20. Despite dire warnings
from DEC engineers that the S-bus could not possibly support a
physically external memory box, Jay Canel of Ampex came to CompuServe
with the first ARM-20 box, plugged it in to our 2050, made one
timing adjustment, then we watched it run for the next six months
without a failure.
    Our next 2050 enhancement was to design a channel interface.
Since the Massbus was patented, and DEC was not granting licenses, we
built directly to the C and E busses. Our "MBX-20" let us connect 300
mb SMD disks to the 2050 using a Telefile controller, instead of
being limited to the 200 mb RP06 (all that DEC offered then).
    By 1978 we had two computer centers - the one in Arlington full of
KI's, and one in Dublin, Ohio, filling up with 2050's. We were not
yet ready to abandon the KI's, but wanted some more horsepower out
of them.  Wilson Mowbray designed a hardware cache memory for the KI
which yielded a 30% improvement in KI speed. Later, Wilson designed a
switching regulator power supply for the KL, which halved it's power
consumption.  Roseann Giordano was so impressed that she sent some
DEC engineers to look at it.  They liked it, but the KL was too near the
end of its product life cycle for DEC to make any changes, even
though we offered to give them the design.
    By 1980 PC's were beginning to assume many of the tasks formerly
done on timesharing systems. Many of our old timesharing
competitors (Cyperhnetics, First Data, On-Line Systems) had been
acquired or disappeared.  CompuServe (which had added the "e" by this
time) was acquired itself in 1980 by H&R Block.  Block wisely let
CompuServe continue with all its plans -- including rolling out a
service for PC users modelled loosely after the European "videotex"
services.  Developed almost clandestinely shortly before the Block
acquisition, it was called "schlock timesharing" by the "professional"
commercial timesharing sales force.  Initially released as "MicroNet"
and later as "the CompuServe Information Service," it grew to be 50%
of CompuServe revenues by 1987, while commercial timesharing evolved
rapidly toward databases, email, and commercial videotex.
    With Block providing financial backing, ComuServe entered the
acquisition business itself.  It's first acquisition was Software
House (the authors of 1022 and 1032 DBMS systems.)  While solidifying
our position in the 10 world with 1022, we also had taken a first step
into the world of Vax with 1032.
    There was some pressure from various quarters to "upgrade" our
hardware to something more modern -- like Vaxes, for instance.
However, by 1986, KL's were less than $20,000; we had our own monitor
and most systems software (except LINK-10 and BLISS-36); we were
able to use current technology disk drives; and we had 100+ manyears of
applications software in XF4 (our own ten-based extended Fortran) and
Bliss-36 -- so how could we justify a change unless 36-bit cpu's
became unavailable?  To be sure that didn't happen, we ordered a
Systems Concepts SC-30 from Mike Levitt.  It arrived in late 1987 (a
bit behind schedule), but came up and ran our operating system with no
more than the expected number of microcode bugs.  (We used Tops-10
paging, which Systems Concepts had not fully tested before).  It worked
well enough that we ordered a total of 10 SC-30's - four of which are
up and running as of this writing; the remainder to be delivered next
year. The venerable KI's (the last of the "lights mentality" machines)
are being phased out to make room for the SC-30's... (and yes, a few
Vax 8550's have snuck in too, for some new applications already
written for Vax).  New interfaces are being designed for both the
KL's and the SC-30's to support faster disks, optical storage, and
new archival storage devices.  Applications development in Bliss-36
and XF4 continues unabated.  At CompuServe, at least, 36-bit computing
has a bright future.