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Whirlwind I
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Vacuum tube computer developed by the MIT
CAPTION: Whirlwind I
Museum of Science, Boston, MA - IMG 3168.JPG
Whirlwind computer elements: core memory (left) and operator console
Product family "Whirlwind Program"^[1]/"Whirlwind Project"^[2]
Release date April 20, 1951 (1951-04-20)
Whirlwind I was a Cold War-era vacuum tube computer developed by the
MIT Servomechanisms Laboratory for the U.S. Navy. Operational in 1951,
it was among the first digital electronic computers that operated in
real-time for output, and the first that was not simply an electronic
replacement of older mechanical systems.
It was one of the first computers to calculate in parallel (rather than
serial), and was the first to use magnetic-core memory.
Its development led directly to the Whirlwind II design used as the
basis for the United States Air Force SAGE air defense system, and
indirectly to almost all business computers and minicomputers in the
1960s,^[3] particularly because of the mantra "short word length,
speed, people."^[4]
[ ]
Contents
* 1 Background
* 2 Technical description
+ 2.1 Design and construction
+ 2.2 The memory subsystem
+ 2.3 Magnetic-core memory
+ 2.4 Vacuum tubes
* 3 Air defense networks
* 4 Legacy
* 5 See also
* 6 References
* 7 External links
Background[edit]
During World War II, the U.S. Navy's Naval Research Lab approached MIT
about the possibility of creating a computer to drive a flight
simulator for training bomber crews. They envisioned a fairly simple
system in which the computer would continually update a simulated
instrument panel based on control inputs from the pilots. Unlike older
systems such as the Link Trainer, the system they envisioned would have
a considerably more realistic aerodynamics model that could be adapted
to any type of plane. This was an important consideration at the time,
when many new designs were being introduced into service.
The Servomechanisms Lab in MIT building 32^[5] conducted a short survey
that concluded such a system was possible. The Navy's Office of Naval
Research decided to fund development under Project Whirlwind (and its
sister projects, Project Typhoon and Project Cyclone, with other
institutions),^[6] and the lab placed Jay Forrester in charge of the
project. They soon built a large analog computer for the task, but
found that it was inaccurate and inflexible. Solving these problems in
a general way would require a much larger system, perhaps one so large
as to be impossible to construct. Judy Clapp was an early senior
technical member of this team.
Perry Crawford, another member of the MIT team, saw a demonstration of
ENIAC in 1945. He then suggested that a digital computer would be the
best solution. Such a machine would allow the accuracy of simulations
to be improved with the addition of more code in the computer program,
as opposed to adding parts to the machine. As long as the machine was
fast enough, there was no theoretical limit to the complexity of the
simulation.
Until this point, all computers constructed were dedicated to single
tasks, and run in batch mode. A series of inputs were set up in advance
and fed into the computer, which would work out the answers and print
them. This was not appropriate for the Whirlwind system, which needed
to operate continually on an ever-changing series of inputs. Speed
became a major issue: whereas with other systems it simply meant
waiting longer for the printout, with Whirlwind it meant seriously
limiting the amount of complexity the simulation could include.
Technical description[edit]
Design and construction[edit]
By 1947, Forrester and collaborator Robert Everett completed the design
of a high-speed stored-program computer for this task. Most computers
of the era operated in bit-serial mode, using single-bit arithmetic and
feeding in large words, often 48 or 60 bits in size, one bit at a time.
This was simply not fast enough for their purposes, so Whirlwind
included sixteen such math units, operating on a complete 16-bit word
every cycle in bit-parallel mode. Ignoring memory speed, Whirlwind
("20,000 single-address operations per second" in 1951)^[7] was
essentially sixteen times as fast as other machines. Today, almost all
CPUs perform arithmetic in "bit-parallel" mode.
The word size was selected after some deliberation. The machine worked
by passing in a single address with almost every instruction, thereby
reducing the number of memory accesses. For operations with two
operands, adding for instance, the "other" operand was assumed to be
the last one loaded. Whirlwind operated much like a reverse Polish
notation calculator in this respect; except there was no operand stack,
only an accumulator. The designers felt that 2048 words of memory would
be the minimum usable amount, requiring 11 bits to represent an
address, and that 16 to 32 instructions would be the minimum for
another five bits -- and so it was 16 bits.^[8]
The Whirlwind design incorporated a control store driven by a master
clock. Each step of the clock selected one or more signal lines in a
diode matrix that enabled gates and other circuits on the machine. A
special switch directed signals to different parts of the matrix to
implement different instructions.^[citation needed] In the early 1950s,
Whirlwind I "would crash every 20 minutes on average."^[9]
Whirlwind construction started in 1948, an effort that employed 175
people, including 70 engineers and technicians. In the third quarter of
1949, the computer was advanced enough to solve an equation and display
its solution on an oscilloscope,^[10]^: 11.13 ^[11] and even for the
first animated and interactive computer graphic game.^[12]^[13] Finally
Whirlwind "successfully accomplished digital computation of
interception courses" on April 20, 1951.^[14]^[10]^: 11.20-21 The
project's budget was approximately $1 million a year, which was vastly
higher than the development costs of most other computers of the era.
After three years, the Navy had lost interest. However, during this
time the Air Force had become interested in using computers to help the
task of ground controlled interception, and the Whirlwind was the only
machine suitable to the task. They took up development under Project
Claude.
Whirlwind weighed 20,000 pounds (10 short tons; 9.1 t).^[15]
The memory subsystem[edit]
The original machine design called for 2048 (2K) words of 16 bits each
of random-access storage. The only two available memory technologies in
1949 that could hold this much data were mercury delay lines and
electrostatic storage.
A mercury delay line consisted of a long tube filled with mercury, a
mechanical transducer on one end, and a microphone on the other end,
much like a spring reverb unit later used in audio processing. Pulses
were sent into the mercury delay line at one end, and took a certain
amount of time to reach the other end. They were detected by the
microphone, amplified, reshaped into the correct pulse shape, and sent
back into the delay line. Thus, the memory was said to recirculate.
Mercury delay lines operated at about the speed of sound, so were very
slow in computer terms, even by the standards of the computers of the
late 1940s and 1950s. The speed of sound in mercury was also very
dependent on temperature. Since a delay line held a defined number of
bits, the frequency of the clock had to change with the temperature of
the mercury. If there were many delay lines and they did not all have
the same temperature at all times, the memory data could easily become
corrupted.
The Whirlwind designers quickly discarded the delay line as a possible
memory--it was both too slow for the envisioned flight simulator, and
too unreliable for a reproducible production system, for which
Whirlwind was intended to be a functional prototype.
The alternative form of memory was known as "electrostatic". This was a
cathode ray tube memory, similar in many aspects to an early TV picture
tube or oscilloscope tube. An electron gun sent a beam of electrons to
the far end of the tube, where they impacted a screen. The beam would
be deflected to land at a particular spot on the screen. The beam could
then build up a negative charge at that point, or change a charge that
was already there. By measuring the beam current it could be determined
whether the spot was originally a zero or a one, and a new value could
be stored by the beam.
There were several forms of electrostatic memory tubes in existence in
1949. The best known today is the Williams tube, developed in England,
but there were a number of others that had been developed independently
by various research labs. The Whirlwind engineers considered the
Williams tube, but determined that the dynamic nature of the storage
and the need for frequent refresh cycles was incompatible with the
design goals for Whirlwind I. Instead, they settled on a design that
was being developed at the MIT Radiation Laboratory. This was a
dual-gun electron tube. One gun produced a sharply-focused beam to read
or write individual bits. The other gun was a "flood gun" that sprayed
the entire screen with low-energy electrons. As a result of the design,
this tube was more of a static RAM that did not require refresh cycles,
unlike the dynamic RAM Williams tube.
In the end the choice of this tube was unfortunate. The Williams tube
was considerably better developed, and despite the need for refresh
could easily hold 1024 bits per tube, and was quite reliable when
operated correctly. The MIT tube was still in development, and while
the goal was to hold 1024 bits per tube, this goal was never reached,
even several years after the plan had called for full-size functional
tubes. Also, the specifications had called for an access time of six
microseconds, but the actual access time was around 30 microseconds.
Since the basic cycle time of the Whirlwind I processor was determined
by the memory access time, the entire processor was slower than
designed.
Magnetic-core memory[edit]
Circuitry from core memory unit of Whirlwind
Core stack from core memory unit of Whirlwind
Project Whirlwind core memory, circa 1951
Jay Forrester was desperate to find a suitable memory replacement for
his computer. Initially the computer only had 32 words of storage, and
27 of these words were read-only registers made of toggle switches. The
remaining five registers were flip-flop storage, with each of the five
registers being made from more than 30 vacuum tubes. This "test
storage", as it was known, was intended to allow checkout of the
processing elements while the main memory was not ready. The main
memory was so late that the first experiments of tracking airplanes
with live radar data were done using a program manually set into test
storage. Forrester came across an advertisement for a new magnetic
material being produced by a company. Recognizing that this had the
potential to be a data storage medium, Forrester obtained a workbench
in the corner of the lab, and got several samples of the material to
experiment with. Then for several months he spent as much time in the
lab as he did in the office managing the entire project.
At the end of those months, he had invented the basics of magnetic-core
memory and demonstrated that it was likely to be feasible. His
demonstration consisted of a small core plane of 32 cores, each
three-eighths of an inch in diameter. Having demonstrated that the
concept was practical, it needed only to be reduced to a workable
design. In the fall of 1949, Forrester enlisted graduate student
William N. Papian to test dozens of individual cores, to determine
those with the best properties.^[10] Papian's work was bolstered when
Forrester asked student Dudley Allen Buck^[16]^[17]^[18] to work on the
material and assigned him to the workbench, while Forrester went back
to full-time project management. (Buck would go on to invent the
cryotron and content-addressable memory at the lab.)
After approximately two years of further research and development, they
were able to demonstrate a core plane that was made of 32 by 32, or
1024 cores, holding 1024 bits of data. Thus, they had reached the
originally intended storage size of an electrostatic tube, a goal that
had not yet been reached by the tubes themselves, only holding 512 bits
per tube in the latest design generation. Very quickly, a 1024-word
core memory was fabricated, replacing the electrostatic memory. The
electrostatic memory design and production was summarily canceled,
saving a good deal of money to be reallocated to other research areas.
Two additional core memory units were later fabricated, increasing the
total memory size available.
Vacuum tubes[edit]
The design used approximately 5,000 vacuum tubes.
The large number of tubes used in Whirlwind resulted in a problematic
failure rate since a single tube failure could cause a system failure.
The standard pentode at the time was the 6AG7, but testing in 1948
determined that its expected lifetime in service was too short for this
application. Consequently, the 7AD7 was chosen instead, but this also
had too high a failure rate in service. An investigation into the cause
of the failures found that silicon in the tungsten alloy of the heater
filament was causing cathode poisoning; deposits of barium
orthosilicate forming on the cathode reduce or prevent its function of
emitting electrons. The 7AK7 tube with a high-purity tungsten filament
was then specially developed for Whirlwind by Sylvania.^[19]^: 59-60
Cathode poisoning is at its worst when the tube is being run in cut-off
with the heater on. Commercial tubes were intended for radio (and
later, television) applications where they are rarely run in this
state. Analog applications like these keep the tube in the linear
region, whereas digital applications switch the tube between cut-off
and full conduction, passing only briefly through the linear region.
Further, commercial manufacturers expected their tubes to only be in
use for a few hours per day.^[19]^: 59 To ameliorate this issue, the
heaters were turned off on valves not expected to switch for long
periods. The heater voltage was turned on and off with a slow ramp
waveform to avoid thermal shock to the heater filaments.^[20]^: 226
Even these measures were not enough to achieve the required
reliability. Incipient faults were proactively sought by testing the
valves during maintenance periods. They were subject to stress tests
called marginal testing because they applied voltages and signals to
the valves right up to their design margins. These tests were designed
to bring on early failure of valves that would otherwise have failed
while in service. They were carried out automatically by a test
program.^[19]^: 60-61 The maintenance statistics for 1950 show the
success of these measures. Of the 1,622 7AD7 tubes in use, 243 failed,
of which 168 were found by marginal testing. Of the 1,412 7AK7 tubes in
use, 18 failed, of which only 2 failed during marginal checking. As a
result, Whirlwind was far more reliable than any commercially available
machine.^[19]^: 61-62
Many other features of the Whirlwind tube testing regime were not
standard tests and required specially built equipment. One condition
that required special testing was momentary shorting on a few tubes
caused by small objects like lint inside the tube. Occasional spurious
short pulses are a minor problem, or even entirely unnoticeable, in
analog circuits, but are likely to be disastrous in a digital circuit.
These did not show up on standard tests but could be discovered
manually by tapping the glass envelope. A thyratron-triggered circuit
was built to automate this test.^[20]^: 225
Air defense networks[edit]
After connection to the experimental Microwave Early Warning (MEW)
radar at Hanscom Field using Jack Harrington's equipment and commercial
phone lines,^[21] aircraft were tracked by Whirlwind I.^[22] The Cape
Cod System subsequently demonstrated computerized air defence covering
southern New England.^[specify] Signals from three long range
(AN/FPS-3) radars, eleven gap-filler radars, and three height-finding
radars were transmitted over telephone lines to the Whirlwind I
computer in Cambridge, Massachusetts. The Whirlwind II design for a
larger and faster machine (never completed) was the basis for the SAGE
air defense system IBM AN/FSQ-7 Combat Direction Central.
Legacy[edit]
The Whirlwind used approximately 5,000 vacuum tubes. An effort was also
started to convert the Whirlwind design to a transistorized form, led
by Ken Olsen and known as the TX-0. TX-0 was very successful and plans
were made to make an even larger version known as TX-1. However this
project was far too ambitious and had to be scaled back to a smaller
version known as TX-2. Even this version proved troublesome, and Olsen
left in mid-project to start Digital Equipment Corporation (DEC). DEC's
PDP-1 was essentially a collection of TX-0 and TX-2 concepts in a
smaller package.^[23]
After supporting SAGE, Whirlwind I was rented ($1/yr) from June 30,
1959, until 1974 by project member, Bill Wolf.
Commemorative plaque on the original Whirlwind building
Ken Olsen and Robert Everett saved the machine, which became the basis
for the Boston Computer Museum in 1979. It is now in the collection of
the Computer History Museum in Mountain View, California.
As of February 2009, a core memory unit is displayed at the Charles
River Museum of Industry & Innovation in Waltham, Massachusetts. One
plane^[clarification needed], on loan from the Computer History Museum,
is on shown as part of the Historic Computer Science displays at the
Gates Computer Science Building, Stanford.
The building which housed Whirlwind was until recently home to MIT's
campus-wide IT department, Information Services & Technology and in
1997-1998, it was restored to its original exterior design.^[24]
See also[edit]
* List of vacuum tube computers
* History of computing hardware
* Laning and Zierler system
* Roger Sisson
* Perry O. Crawford Jr.
* Lightgun (Whirlwind) lightpen designed for Whirlwind
References[edit]
1. ^ Redmond, Kent C.; Smith, Thomas M. (1980). Project Whirlwind: The
History of a Pioneer Computer. Bedford, MA: Digital Press.
ISBN 0-932376-09-6. Retrieved 2012-12-31.
2. ^ "Compaq donates historic SAGE, Whirlwind artifacts to museum".
MITnews. September 26, 2001. Retrieved 2013-08-12.
3. ^ "IBM Benefits from the Cold War". Grace Hopper and the Invention
of the Information Age. Book Baby. 2015.
4. ^ Larry Watkins (May 1982). "A DEC History of Minicomputers".
Hardcopy. pp. 12-19. "Of these, speed is the least important factor
from a historical standpoint .. people are a very important factor
.. Ken Olsen .. Ben Gurley"
5. ^ Ross, Douglas T.; Aspray, William (21 February 1984), An
Interview with DOUGLAS T. ROSS (pdf transcript of vocal recording),
retrieved 2013-08-12
6. ^ Project Whirlwind is a high-speed computer activity sponsored at
the Digital Computer Laboratory, formerly a part of the
Servomechanisms Laboratory, of the Massachusetts Institute of
Technology (MIT) by the US Office of Naval Research (ONR) and the
United States Air Force. IEEE Computer Society
7. ^ Everett, R. R. (1951). "The Whirlwind I computer". Papers and
Discussions Presented at the December 10-12, 1951, Joint AIEE-IRE
Computer Conference: Review of Electronic Digital Computers. ACM:
70-74. doi:10.1145/1434770.1434781. S2CID 14937316. Retrieved
2013-08-12.
8. ^ Everett, R. R.; Swain, F. E. (September 4, 1947). Report R-127
Whirlwind I Computer Block Diagrams (PDF) (Report). Servomechanisms
Laboratory, MIT. p. 2. Archived from the original (PDF) on
2006-09-08. Retrieved 2012-12-31. "The basic impulse rate for
operation of the computer will be one megacycle. [...] The
Whirlwind I Computer is being planned for a storage capacity of
2,048 numbers of 16 binary digits each."
9. ^ Corbato, F. J. (14 November 1990), An Interview With Fernando J.
Corbato (pdf transcript of vocal recording), retrieved 2013-08-12
10. ^ ^a ^b ^c Redmond, Kent C.; Smith, Thomas M. (November 1975).
"Project Whirlwind". The MITRE Corporation. p. 11.6. Retrieved
2016-07-22.
11. ^ "2. Whirlwind I". Digital Computer Newsletter. 2 (1): 1-2.
1950-01-01. Archived from the original on March 11, 2021.
12. ^ Peddie, Jon (2013-06-13). The History of Visual Magic in
Computers: How Beautiful Images are Made in CAD, 3D, VR and AR.
Springer Science & Business Media. pp. 81-82. ISBN 9781447149323.
13. ^ Angeles, University of California, Los; Inc, Informatics (1967).
Computer graphics; utility, production, art. Thompson Book Co.
p. 106.
14. ^ Boslaugh, David L. (2003-04-16). When Computers Went to Sea: The
Digitization of the United States Navy. John Wiley & Sons. p. 102.
ISBN 9780471472209.
15. ^ 10 short tons:
+
Weik, Martin H. (December 1955). "WHIRLWIND-I". ed-thelen.org. A
Survey of Domestic Electronic Digital Computing Systems., 20,000
lbs:
+
Weik, Martin H. (June 1957). "WHIRLWIND I". ed-thelen.org. A Second
Survey of Domestic Electronic Digital Computing Systems.
16. ^
http://dome.mit.edu/bitstream/handle/1721.3/38908/MC665_r04_E-504.p
df^[bare URL PDF]
17. ^
http://dome.mit.edu/bitstream/handle/1721.3/39012/MC665_r04_E-460.p
df^[bare URL PDF]
18. ^ "Full Page Reload".
19. ^ ^a ^b ^c ^d Bernd Ulmann, AN/FSQ-7: The Computer that Shaped the
Cold War, Walter de Gruyter GmbH, 2014 ISBN 3486856707.
20. ^ ^a ^b E.S. Rich, N.H. Taylor, "Component failure analysis in
computers", Proceedings of Symposium on Improved Quality Electronic
Components, vol. 1, pp. 222-233, Radio-Television Manufacturers
Association, 1950.
21. ^ Jacobs, John F. (1986). The SAGE Air Defense System: A Personal
History (Google Books). MITRE Corporation. Retrieved 2013-08-12.
22. ^ Lemnios, William Z.; Grometstein, Alan A. Overview of the Lincoln
Laboratory Ballistic Missile Defense Program (PDF) (Report). p. 10.
Retrieved 2012-12-31.
23. ^ Pearson, Jamie P. (1992). "dec.digital_at_work" (PDF). Digital
Equipment Corporation. p. 3.
24. ^ Waugh, Alice C. (January 14, 1998). "Plenty of computing history
in N42". MIT News Office.
External links[edit]
* Whirlwind documentation List of Bitsavers.org webpages related to
Whirlwind
Records
Preceded by
-
World's most powerful computer
1951-1954 Succeeded by
IBM NORC
Authority control: National libraries Edit this at Wikidata
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71.09667DEGW / 42.36167; -71.09667
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