abstract: Burroughs large systems memorabilia, B7800 parts
author: Ralph Klimek
date: Mon Apr 7 18:05:00 EST 2008
this article is copyleft, no rights are reserved, logos , trade
marks, however, clearly still belong to their respective owners
My involvement with Burroughs and the mainframe worlds was from late
1985 through to 1990 when by employer ended its usage of large
mainframe systems and replaced it with various minicomputers and
migrated the legacy databases. There I labored under the steady and true gaze of the
great Mr Bruce A. Seaman one of natures gentlemen and the greatest
engineering manager that I
have had the privilege to work for.
In that time I performed engineering maintenance functions on the
mainframe and its peripherals. Sadly very little of it remains, no
documents from that time have survived and only a few relics and only
one museum piece remains from that era. This was well before
the days of the web, near infinite disk storage and digital cameras ,
so all thats left are rapidly fading memories.
I have come to believe that Monash University may have been the
only organization on the planet that did total hardware maintenance of
it Burroughs Large Systems completely in house. I wonder how true
this actually is ? Were there others ?
This piece of the right hand portion of the front panel from a
Burroughs B7800 CPM (central processing module) now decorates my garage
door where it awes my enemies and impresses my friends.
My souvenier of the
CPM. In this design, every register and flip flop was brought out to
the front panel. Each LED had about 16 different meanings depending on
the switch settings. The display was allways on and looked magnificent.
You would walk amongst rows of these panels, it was like the imagined
space ship main battle station of the Death Star. It was a
crowd pleaser at open days and I am sure that this display made the job
of Burroughs salesmen so much easier. As an engineering tool, it was
usefull but not essential. We had a B800 mini computer whose only job
was to read the front panel and tell us that led 27, row18, panel 2 was
off. We would walk around and sure enough the led was in the wrong
state. Very powerful, wise and all knowing it made us engineers
|The Burrough's B-Line an in house journal from the early sixties. This is pioneering computing at its best|
click me to read the entire edition
|an earlier edition of the Burroughs B Line|
The smaller left hand panel of the Burrough B7800 IOM, the Input Output
Module was a standalone processor that handled all interactions with
the peripherals; disk, tape, printers, TTYs
This is a head assembly of the head per track disk above (see images in The B-line) The
ruler is a 15 inch||One disk from a
controller as distinct from "PACK" The "DISK" was this massive one head
per track monster. Total capacity was only 5Megabytes but was damned
fast because there was no seek delay. On this was implemented some of
the industries very first effective virtual memory, as this monster was
still cheaper than core or the new fangled solid state memory. |
above image shows a plane of B5500 magnetic core memory, image courtesy
of Mr Alan Thorne who actually used it ! See the irregular spacing of
the rather large toroids, for this core plane was hand threaded. The
higher density core plane, elsewhere was machine threaded and is more
These core planes were made in Hong Kong,
presumeably by the poor folks that had escaped from communist China and
would do this highly detailed and tedious work for nothing more than a
beating, a handfull of rice and a vague promise that things might get
better. Click on this image to get the full resolution.
The console from a
Pack Driver Controller. There were two redundant controllers in every
B350 controller cabinet. The controller was a B700 minicomputer in its
own right. The console could be inserted and removed while online. It
was removed to discourage "ge-finger-poken". I used these
regularily to perform disk pack maintenance after a special controller
program had been loaded either online or from a Kansas City standard
cassette. There was a hard wired writable control store ram diagnostic in this device.
boards from the BX350 disk pack drive controller. All that
glitters is sometimes gold! The view into a full card cage of these was
like looking into aladin's cave.
This card was one of about a thousand that came from the memory
cabinets. The memory chips are intel 4kbits by 1 .
Burroughs was maxed out with 8 Megabytes. The Burroughs had
good ECC and could tolerate a small number faulty chips. We spent a
good portion of our time replacing many of these rather forgetfull
Engineering Display cards. These would be clamped onto edge connectors
and you slided a lable into the label holder which told you what the
lights meant for that particular card. In the B7800 they were used only
on the Peripheral Control Cabinets
Core memory plane from a Burroughs DCP, one of about 20 such boards in
click and zoom in on this
A PCC cabinet line driver interface card
Console card from the
This mainframe relic is on public display in biulding 28, the
Mathematics Biulding at the clayton campus of Monash University under
the stairwell at the main entrance. Be sure to visit it if you have
business at Monash. Its usually open during the annual open
A view of the Burrough
mainframe and backplane. The backplane was a robot wire wrapped marvel
and maintenance nightmare. All done with twisted pair wire, all colored
alike. We we had to perform modifications ( hardware patching! none of
this download new firmware nonsense) we used yellow wire wrap wire to
help remind ourselves where and what we had done. Wire wraps could be
up to four levels deep. Dead wires were left in place because it was
impossible to disentangle them. Worst faults were intermittant ones
whereby insulation would be cut through by adjacent sharp wire wrap
pins. The small floating PCBs are clock distribution modules.
The awesome backplane. Source of many intermittant faults and surely
the last word in heroic complexity.
Detail from above. The dust dates from 1989 when this machine
powered down for the last time. This is a clock distribution board, not
a delay line as many erroneously thought. Some of those wires are mine.
Some views of the PSU There were about 40 of these in each
mainframe cabinet. They took a raw DC input of 120Volts and a
pioneering switchmode power regulator transformed it to 4.8V or -2.0V.
The two coils visible here are current shunts for automatic short
circuit constant current mode running. You cannot parallel voltage
sources, they must have some resistance and these coils of bronze wire
The primary DC supply was derived from switched SCR rectifiers that
were directly connected to large 3 phase step down transformers and
these were direct on line. Everytime the lights blinked we
to ourselves about our fates and attended to repair 3 or 4 of these
units when the output transistors had been popped by a surge or other
transient. We became very good at replacing power transistors in a
hurry. A tripped breaker at the front told us the unwelcome news. Often
the machine would continue to run with up to six dead PSUs.
The many power supplies sat in these racks at the top of the machine,
behind the front display panels.
The blue sheets are solid aluminum bus bars that carried about 5
kilo-amps of 4.85V and -2.0 V to the card cage. The unit shown here is
a negative 2.0 Volt psu that would have joined its forty odd companions
in this rack . Each supply could source 135 Amps under normal conditions
A sadly empty card cage
The completely wired wrapped cards, no two were alike. This was not a
machine for board jockeys.
Wire wraps were two deep and productions cards were wrapped by robot.
This board and its hundreds of companions was biult from a hybrid
mixture of CTuL logic
and TTL logic for more rarely used MSI functions. Chip makers were
Fairchild and ITT.
The above two images are
from one of
the hundreds of circuit cards from the Burroughs B7800 CPM and IOM
mainframes. The chip family is the little emulated and not
lamented CTuL family that was made on special order from Fairchild and
ITT. All the boards were totally wire wrapped with the ICs soldered in
place, the chips were never socketed. The wire wrap was two deep per
post. The close up shows a clock distribution amplifier, every card had
at least one of these. We had to perform chip level repairs on these
boards. There were no schematics. What we had we the so
LOCAL books (Logical and Chip Analysis) which had a typographical
tabular convention that specified the logic equations for the board and
the complete wire map in tabular form. From test vectors injected by
the B800 mainenance processor the machine and the board called be put
into a state one clock cycle before the error vector. We traced the
faulty logic state back from the front panel, to one or more cards and
finally to the chip or wired OR signal. Some horrible wire OR signals
had over one hundred terms and could take days of very
probing and thinking. Intermittant faults were common. When working
this way with a suspect board out of the card cages on an extender we
would be exposed to the full blast of the underfloor cooling and this
was highly unpleaseant, the set point temperature was 12 degrees C.
Cooling failures were potentially diasterous and one of my
first projects was to construct an overtemperature detector and remote
CTul was somewhat like ECL ( see
my ECL rant
) but yet completely unlike it. It was a strange RTL-like
with open emitter output. It was incredibly power hungry, a
chip left powered up without a hurricanes' worth of cold air blasting
over it could get too hot to touch. I dont believe that anybody other
than Burroughs ever used this logic family. They choose to use this
logic family very early and only gave it up when the A10 series
mainframe was released make of TTL. The logic family was
fast. The B7800 master clock ran at 8Mhz.
There were only SSI functions available in the family, but it was sort
of TTL compatible and the B7800 used TTL gates for things like bipolar
memory. Logic supplies were 4.75 volts and negative 2Volts.
CTuL gates did not have gain, and that meant that after a logic signal
had propagated through 3 levels of logic a buffer or amplifier would be
required to regenerate the logic level.
CTuL first appeared in 1965 and the images below are from an ancient
Fairchild manual. It predates TTL by about 10 years. I suspect it was developed to get around Motorala ECL patents.
plate from a
type 235 quad density disk pack drive unit. The power consumption was
no engineering overestimation it was quite real. Most of the
power consumed was utilized in spinning the 12 fourteen inch diameter
platters of the disk pack at mains synchronous speed, the power
consumed was mostly the induced drag in air. The air was given a
significant centrifugal acceleration and this facilitated both cooling
and cleaning the air gap space. The suction induced at the core of the
pack would help suck air through the absolute filter that required
changing every six months or so. This particular drive unit
170 Megabytes of formatted space.
A nd for old time sake,
here is the CANDE manual, but only on microfiche. No , you cannot read it, my scanner is not that good!
you zoom in deeply you might just be able to make out the famous
railroad diagrams that "explained" the sometimes bizarre syntax.
Burroughs chip house code to commercial equivalents list
These pages are burroughs house part number codes to commercial
equivalents. I prepared this list sometime in 1987 to aid myself in
sourcing replacement commercial parts. Burroughs then liked to charge
$50 for a 7400 quad nand gate because it had their house code
it...and off course, your mainframe wouldnt work unless it had the
genuine burroughs part...wouldnt it now!
I have provided this list as a service to hobbyists and radio hams that
may come across discarded computer boards packed with assorted TTL
chips that are useless unless you can find the commercial part numbers.
The list was constructed largely from schematics, order books and
sometimes chip manufactures would print the burroughs house code on top
of the chips but also print the commercial type numbers underneath!
This list is not available in machine readable form.
|Most of my digital projects documented elsewhere were built with
discarded burroughs chips|
Here is my complete scan of the B6700 systems architecture manual
Here are some images of Burroughs places and people kindly sent to me by Mr M Morreal a former manager at
Burroughs. Here are some of the people behind the Burroughs Large Systems machines
|Am image of the Treddyfrin plant|
click them to download full res images
Now thats some real history. Dont forget to have a look at a complete edition of B-Line, and B-Line-2 the corporate journal from the mid sixties
|emails welcomed at|
my warm thanks to all that have written so far.
record: Mon Sep 29 18:52:23 EST 2008 added partial scan of B6700
architecture manual, add link to the B-Line journal Fri
May 29 20:00:35 EST 2009 added image contribution from Mr M Morreal.
Fri Jun 5 19:05:39 EST 2009 added new link to scans of Bline2