The Remington Rand Univac LARC
by Charles Cole
The Remington Rand Univac LARC (Livermore Advanced Research Computer) computer system was delivered to the Lawrence Livermore
National Laboratory (then called the University of California Radiation
Laboratory) in March of 1960. There had never been anything built on the scale
of this computer. It was massive both in physical size and computational
capability. A new building (now numbered B-117) was constructed just to house
it. Physically, it consisted of four major cabinets. Each cabinet was
approximately twenty feet long, four feet wide, and seven feet tall. In addition
there was an array of twelve floating-head drums, each approximately four feet
wide, three feet deep and five feet tall. There were eight tape units that used
metallic tape (each tape weighed about ten pounds), a punched-card reader, and a
large printer. Operation of the system was controlled from a central console
with lots of flashing lights, switches, digital readouts, and pushbuttons.
Teletype units (with paper tape readers / punches) provided direct
communications with the computer. The control console also provided an array of
toggle switches to feed direct commands to the system.
The four hardware cabinets consisted of: the I/O processor unit (one cabinet)
where all information destined to and from the drums, tapes, printers, console,
etc. was routed and controlled; the computing unit (one cabinet, where
computational activity occurred); and memory (two cabinets, each with 16K of
ferrite core memory). Later, a third memory cabinet was added to expand local
memory.
Storage devices were state-of-the-art for the day. The drum units were rotating
cylinders coated with a magnetic material. Storage density was 450 binary digits
per inch. Each cylinder was 27-1/2 inches long and 24 inches in diameter,
providing for a storage capacity of 250,000 LARC words (12 decimal digits each)
per drum. Twelve drums were included in the Livermore system. The drum surface
was divided into 100 circumferential bands. Each band was divided into 25
sectors (a sector could hold 100 LARC words). A data transfer could begin at any
sector boundary. Each band was made up of six parallel tracks; five for the
digit of information, and the sixth for a permanently recorded sector address.
The single floating head could be positioned over any band for reading or
writing. Moving the head across the drum from one band to the next took 70
milliseconds. If it was to be repositioned more than one band, the speed
increased to 50 milliseconds per band. Reversing the direction of travel took 10
milliseconds. There were two independent controllers (called synchronizers) for
read operations, and one for write. With the independent controllers one drum
could be repositioning its head, while a different unit was reading data,
thereby significantly improving data recovery time. A complete band of
information could be transferred between the drum and main memory in about 90
milliseconds after positioning was completed.
The magnetic tape of choice on the LARC computer was made of metal. There were
eight magnetic tape units on the LARC, although the system was designed to
support up to forty units. Standard tape reels were either 1500 or 2400 feet in
length (8-inch diameter, or 10-inch diameter reels). A 2400-foot reel would
theoretically hold approximately 600,000 LARC words. The units could record at
densities as high as 250 characters per inch, although on the LARC delivered to
Livermore this density was limited to 208 characters per inch. Data was recorded
in blocks of ten words each. There was a space between each recorded block on
the tape so, in actual practice, a single tape would hold approximately 450,000
LARC words. Data was recorded in 8-track parallel mode; 7 tracks representing
the character, and the eighth a control pulse. The tape moved at 100 inches per
second. Full acceleration or deceleration took about 5 milliseconds.
The printer provided a maximum of 130 characters per line (ten characters per
inch). It supported a set of 51 alphanumeric characters. A single line could be
printed in approximately 80 milliseconds with a speed of 600 single-spaced lines
per minute. Quite a respectable print rate considering that the console printers
(there were two on the LARC system, called Flexowriters) provided only 10
characters per second. The paper feed mechanism moved the paper a line at a
time, and each advance took 20 milliseconds.
Computationally, the LARC was a marvel or, maybe, a monster. Arithmetic was
performed in decimal mode, which was the custom at Univac at the time (the
Univac I also performed decimal arithmetic). The LARC employed twelve decimal
digits. A five-bit register represented the numerical value in each digit.
Arithmetic was performed using these coded digits in a dizzying array of
temporary storage registers that saved the initial integer values as well as
partially computed results. There were storage registers, shift registers, and
result registers that could store information for repetitive calculations that
would ultimately yield an answer. Calculation speed was also dizzying: a 12 x 12
digit addition or subtraction could be accomplished in 4 microseconds, while a
12 x 12 multiplication would complete in twelve microseconds. Division took a
bit longer.
The LARC offered arithmetic to 22 decimal digits, and performed floating-point
arithmetic using the uppermost two decimal digits to represent the power of the
number in the remainder of the field. Thus, floating point operations offered
values of ten to the power of plus or minus ninety-nine.
The LARC was the first "supercomputer," and demonstrated the exciting promise of
computing as a scientific tool. It also was instrumental in demonstrating why
binary arithmetic (rather than decimal) was a far superior option for computers.
But, in those days, such issues were still being sorted out.
The LARC arrived at the Lawrence Radiation Laboratory in 1960, after a three-
week truck ride from Philadelphia (a caravan of five 18-wheelers crossing the
country in the wintry conditions of February and early March). Accompanying the
hardware was a crew of approximately forty installers from Remington Rand. These
included electricians, plumbers, air conditioning experts, computer engineers,
technicians and so on. It took more than two months to complete the physical
installation and another two months to get the computer working again. Following
installation, there was the nerve-wracking task of passing a rigorous
"acceptance" test. This test required that the computer satisfy certain pre-
specified performance criteria before the Laboratory would accept it. An
engineering / technician work crew of four individuals remained at Livermore for
the additional seven months it took to pass the acceptance test.
Following acceptance, the computer was placed into production service, which
meant that programmers and scientists could schedule "run time" on the system.
This generally took the form of a programmer loading his problem on the system
and then sitting at the console to run and monitor its execution. This was often
a most frustrating activity as three separate significant factors conspired to
weaken the likelihood of success: 1) The programmers were only beginning to
learn how to use a computer for their very complex problems; 2) The operating
system was newly developed by Laboratory Computation staff and still suffered
occasional "glitches," and, 3) The hardware was temperamental. While most
operating efforts were successful (generally yielding an acceptable result or
some good clues as to what was going wrong), not all were clear. Fortunately,
the system designers had constructed the operating console to allow for
extensive bug shooting.
On infrequent occasions, major hardware modifications were required. The
computer would be taken out of service and engineers and technicians would
install the necessary upgrades. This often took the form of rewiring the
backplane of the computing unit. Although the LARC was the first computer to
utilize printed circuit technology (and, for that matter, transistor technology
on a large scale), such processes were at a very rudimentary stage. Printed
circuit interconnections existed only within a given circuit board. All
connections between printed circuit boards were hardwired. This meant that in
the backplane there was a wire for every point-to-point connection in the
computer. Literally thousands and thousands of wires, all placed in as direct a
line as possible from source point to destination point. The end result was a
wiring mesh of many thousands of wires layered on top of each other, all on top
of the backplane connection points. In places the stack of wires reached a depth
of six to eight inches. A modification would require that some of those wires be
removed or rerouted, and new wires installed. There was a unique set of tools
for this purpose. A long hollow tube, with a light at the end and a magnifying
glass (called a floroscope) was used by the technicians to burrow through the
wiring mesh to the backplane to identify appropriate wires to remove, and to
locate holes in the backplane where new wires were to be installed. Having found
the appropriate wire or hole, the technician would then use long-neck pliers to
remove a wire connection, or a long screwdriver-type tool modified for the
purpose, to forcefully insert a new connection. This process required that the
technician peer through the floroscope and guide the other tools to their proper
position and execute the required action. This was a very tedious operation and
could become quite time consuming. It was also fraught with obvious peril. An
incorrectly removed or installed wire would not only prevent the new function from performing as intended, but would very likely create a problem with an
operation that was functioning perfectly before the modification. Merely
burrowing through the deep stack of wires would sometimes unintentionally
dislodge other wires leading to further problems. The technicians most skilled
in these modifications were very popular at the time.
Still and all, the LARC worked amazingly well, considering the nature of its
radical new high-end computer design in the very early days of computer design
and development. As mentioned above, the hardware was constructed of all
discrete components: transitors, resistors, capacitors, and such. Maintenance of
the individual circuit boards was performed at the component level. Individual
transistors were replaced when faulty, and other electronic circuitry was
repaired at that same micro level. Finding a failed part was quite a challenge
as the fault had to be traced to the component level for repair. To aid in
troubleshooting failures the printed circuit boards could be mounted on
"extenders" and reinserted in the computer. This allowed observation of the
inner working within the board circuitry. Unfortunately, extending the circuit
board added several inches of length to the signal paths and, on rare occasions,
would introduce a problem quite different from the one being analyzed.
But, despite all its flaws and shortcomings, the LARC was a useful new tool
employed in the quest for advances in the scientific challenges of the Lawrence
Radiation Laboratory. Livermore computer programmers developed the software to
control data storage on the massive drum units. This experience proved most
valuable in later efforts at developing software to control larger, more modern
large-scale storage systems. Likewise, developing the software to control system
functions was important training for the computer systems programmers that would
later develop the operating systems for the Control Data computer line, and
later the Cray computers. Perhaps most important was the experience garnered by
the scientists who learned how to use the power of computing to simplify and
visualize the problems they are still addressing today.
There are many milestones of note in the computing history of the Lawrence
Livermore National Laboratory. The LARC computer system surely ranks alongside
all the other major innovations in the "art" of supercomputing.
Chuck Cole joined Remington Rand Univac in 1959 just as the computer "revolution" was getting started. The Univac I, the first commercially available general-purpose computer, was in full production at Remington Rand. An early serial number had been delivered to Livermore. At the same time the Livermore Advanced Research Computer (LARC) was being built and debugged at eh Univac plant in Philadelphia, with scheduled delivery already several months late. Chuck was assigned to the LARC project, which eventually led to his assignment to Livermore Lab, and subsequently to his employment there (1963). Chuck left the Laboratory in 1972 to work on a project to install, checkout, and make operational the Illiac IV computer system, at Ames Reasearch Center in Mountain View. He worked on that project until 1975, when he returned to Lawrence Livermore.
In his 30+ years at Lawrence Livermore Lab, he enjoyed a widely diverse set of assignments, ranging from maintenance duties on the LARC, to an eventual appointment as a Deputy Associate Director in Computation Directorate. In between, the assignments included appointment as one of the initial members of a team that developed and deployed the "Octopus Network", a forerunner of the distributed computing environment of today. He was Supervisor of a computer operator group that, at one time, numbered more than a hundred. He formed the Laboratory’s first computer security organization and managed that group, and the growing demand for ever more rigorous computer security, for more than 10 years. In this assignment, he formed an important bridge between the DOE Contractor community and the various federal computer security management and oversight organizations, particularly within the Department of Energy. In 1989, he formed the Computer Incident Advisory Capability group to respond to the ever growing threats fostered by the Internet and global connectivity. In 1992, he served a brief appointment to DOE Headquarters supporting their computer security organization. He returned to the Laboratory to accept an appointment as Deputy Associate Director for Operations and Assurance under then Computation Associate Director Bob Borchers. He served in this assignment under a succession of Associate Directors until his retirement in December, 1997.
For more information: