How Did They Get to the Moon Without PowerPoint?

Mordechai (Moti) Ben-AriDepartment of Science TeachingWeizmann Institute of Sciencemoti.ben-ari@weizmann.ac.il

Keynote speech at the Finnish Computer Science Society, May, 2003.

1 Developing a Technology

Let me start with a description of one of my firstfull-time jobs:

I developed a technology for data min-ing in order to consolidate enterprise-customer relations.

Since I held that job in the early 1970s, clearly Iwould not have described my work in this terminol-ogy! What I actually did was:

I wrote a program that read the systemlog, computed usage of CPU time andprinted reports so that the users couldbe billed.

My point in this talk is that hi-tech in general andcomputer science in particular did not begin in the1990s, but that we have been doing it for decades.I believe that today’s students are being fed a lot ofmarketing propaganda to the contrary, and that theyhave completely lost a historical perspective of ourdiscipline. I further believe that we have a respon-sibility as educators to downgrade the hype and togive our students a firm background in the scientificand engineering principles of computer science.

The idea for this talk came to me while readingthe hi-tech supplement that appears occasionally ina local newspaper. The supplement has a sectionin which they profile new startup companies, andinvariably these companies “develop a technology,”though as far as I can understand from the short pro-files, they have simply designed and constructed abox of electronics or a computer program. So whatis a “technology”? Here is one extreme view:

Basically, microchips are merely a tech-nical improvement over clay tablets.

The invention of writing, however,was the invention of an entirely newtechnology.[3, p. 9]

There is something to be said for this definition:do you remember those old movies that show “typ-ing pools,” where rows and rows of people, usuallywomen, sat pecking away at keyboards all day?

Well, things haven’t changed all that much!

I wouldn’t go so far as to claim that microchipsare a mere “technical improvement,” but I certainlycan’t accept that every new gadget or program is a

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new technology. Here is a list of a few inventionsthat I would classify as new technologies: fiber op-tics, flash memory, celluar communication, public-key cryptography, functional and logic program-ming, packet protocols, fault-tolerant algorithms.What is common to all these “technologies” is thatthey brought about a radical new way of solvingproblems, and that they stimulated research and de-velopment that continued for many years.

2 The Internet Revolution?

If there is one system that epitomizes the new hi-tech world, it is the Internet. It enables us to engagein shopping, exchanging messages and sex, whichare things we couldn’t do before. Ask your studentswhen the Internet was invented and I wouldn’t besurprised if their guesses averaged about 1990. Itis therefore highly instructive to actually look at atimeline of the milestones of its development. I’llonly list a few of the major early milestones and re-fer you to [10] for more detail.

• 1961 - First paper on packet switching byLeonard Kleinrock.

• 1968 - Bolt Beranek and Newman, Inc.(BBN) was awarded the Packet Switch con-tract to build Interface Message Processors(IMPs). 1

• 1969 - ARPANET was commissioned by DoDfor research into networking. The first pack-ets were sent by Charley Kline at UCLA as hetried logging into SRI; the system crashed asthe letter G of LOGIN was entered.

• 1971 - Ray Tomlinson of BBN invented anemail program to send messages across a dis-tributed network.

• 1973 - Bob Metcalfe’s Harvard PhD Thesisoutlined the basic idea for Ethernet. The con-cept was tested on Xerox PARC’s Alto com-puters, and the first Ethernet network wascalled the Alto Aloha System.

• 1973 - The File Transfer specification andNetwork Voice Protocol specification werepublished.

• 1974 - Vint Cerf and Bob Kahn published“A Protocol for Packet Network Interconnec-tion,” which specified in detail the design of aTransmission Control Program (TCP).

The relatively recent invention of web browsers isthus mere syntactic sugar on a very mature technol-ogy.

To be fair, there is some justification for lookingupon the Internet as a new technology. In 1993-4, Iattempted to write a program (excuse me, develop atechnology) and found a startup company to marketit. In order to obtain a connection to the Internet,I was required to receive permission from the Min-istry of Communications, because at that time theonly connections were through an inter-universityhub and so I had to prove that I was engaged inR&D! Of course, this merely shows that the obsta-cles to the spread of the Internet were political andeconomical, not technological.

There are many visionaries who have held outextravagent promises for our wired future, not theleast, ex-vice president of the US Al Gore with hisinformation superhighway. Here is an example ofsuch a utopian vision from Michael Dertouzos ofMIT:

A common bond reached through elec-tronic proximity may help stave off fu-ture flareups of ethnic hatred and na-tional breakups.

Here are some additional quotes. Do you knowwhen they were written?

It is impossible that old prejudices andhostilities should longer exist, whilesuch an instrument has been created forthe exchange of thought between all thenations of the earth.

[It] may not affect maganzine literature,but the mere newspapers must submit todestiny, and go out of existence.

The merchant goes home after a day ofhard work and excitement to a late din-ner, trying amid the family circle to for-get business, when he is interrupted bya [message] from London, ..., and thepoor man must dispatch his dinner ashurriedly as possible in order to send offhis message to California. The business

1US Senator Edward Kennedy congratulated BBN on ecumenical Interfaith Message Processor, which shows that you can’t trustpoliticians to understand technology.

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man of the present day must be contin-ually on the jump[.]

These are clearly utopian visions that high-technology will bring us peace, brotherhood andthe paperless office, though instant communicationthroughout time zones will cause extreme stress inthe work environment.

And here is a characterization of the monopolis-tic practices of the leading company:

Not surprisingly, the company regardedits near monopoly as a good thing.Far from encouraging progress [theCEO] claimed, competition between ri-val companies had actively hinderedit. . . . [The company] insisted that itsmonopoly was in everyone’s interested,even if it was unpopular, because itwould encourage standardization.

Is the author talking about Bill Gates and Microsoft?In fact, the quotes are taken from mid-19th cen-

tury commentary on the use of the telegraph, andthe monopolist CEO was William Orton of WesternUnion. Here is how Thomas Standage characterizesthe introduction of the telegraph [8, p. vii-viii]:

A new communications technology al-lowed people to communicate almostinstantly across great distances. It rev-olutionized business practice, gave riseto new forms of crime, and inundated itsusers with a deluge of information. Ro-mances blossomed, secret codes weredevised and cracked. The benefits ofthe network were relentlessly hyped byits advocates and dismissed by the skep-tics. Governments and regulators triedand failed to control the new medium.A technological subculture with its owncustoms and vocabulary was establish-ing itself.

If I may be allow to quote from the Bible: Mita onollut, sita on tulevinakin aikoina, mita on tapahtunut,sita tapahtuu edelleen: ei ole mitaan uutta auringonalla [Saarnaajan kirja 1(9)].2 In passing, it is worth-while noting that celluar communication is not at alla new technology. The concept was first proposed atBell Labs in 1947, and the first portable cell phonecall was made by Martin Cooper of Motorola on 3

April 1973. He placed this call to Joel Engel, Headof Research at Bell Labs, which was also trying todevelop the technology. Clearly, it takes some timefor new technologies to mature and to be widely ac-cepted, but while celluar communication is certainlya new technology, it does not follow that if you adda camera to a cell phone, then you have developed anew technology. This is just normal development ofa mature technology and we will have to wait to seeif it will be successful in the marketplace or not.

I want to make it clear that I am not a Luddite.The Luddites were English workers who protestedthe changes of the Industrial Revolution, destroyingwool and cotton mills early 19th century. The Britishgovernment suppressed the riots, executing 17 menin 1813. Since then, the term Luddite has come todenote one who opposes advances in technology.

I make my living from computers and alwayshave done so. I routinely use the Internet and can’tbear to be away from my email for more than a dayor so at a time. Furthermore, I have the all the mod-ern gadgets: a cell phone, a Palm Pilot and a lap-top computer. I’m not a Luddite. But I believe thatI have the perspective to see these gadgets as meretools and not as a road to utopia.

2For non-Finnish speakers: The thing that hath been, it is that which shall be; and that which is done is that which shall be done:and there is no new thing under the sun. [Ecclesiastes 1:9]

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3 Computer Science

Unfortunately, I believe that we have also lost per-spective in computer science. Each new system istrumpted as a new technology, even though it mayjust be repacking of well-known technology. Let megive as an example the Java programming languageand system. First, let me say that while Java is notone of my favorite languages, I believe that it is quitewell-designed and I use it extensively in teachingand for developing software tools. But I cannot joinin the hype of Java as something new; it is simplyan excellent packing of technologies that have beenwith us for decades, among them:

• Compilation to a virtual machine - Pascal-P(1974).

• Object-oriented programming - Simula(1964).

• Concurrency within the language - ConcurrentPascal (1974).

• Library within the language - Smalltalk(1969).

Even the cryptic syntax is taken from C which wasdeveloped in 1971. As far as I know, the only majorinnovation in Java is its built-in support for security.

If we take a look at the new ACM/IEEE cur-riculum proposal, we can see an increased emphasison artifacts and specific applications. The proposaldivides the “computer science body of knowledge”into the following 14 fields [1]:

• Discrete Structures

• Programming Fundamentals

• Algorithms and Complexity

• Architecture and Organization

• Operating Systems

• Net-Centric Computing

• Programming Languages

• Human-Computer Interaction

• Graphics and Visual Computing

• Intelligent Systems

• Information Management

• Social and Professional Issues

• Software Engineering

• Computational Science and Numerical Meth-ods

When I look at the detailed list of topics innet-centric computing, human-computer interaction,graphics and visual computing, intelligent systems,information management and software engineering,I do find in each field a couple of topics with signifi-cant scientific content, but most topics are concernedwith specific applications and artifacts that are likelyto become outdated. I know that students considerthese to “new technology,” but I would much pre-fer that they be taught more basic computer scienceand mathematics, as well as the basic concepts ofother fields such as electronics or economics. I amreminded of a project leader at an aerospace com-pany who once told me that in his experience, it iseasier to teach computing to a physics major than itis to teach physics to a computer science major.

4 How Did They Get to theMoon?

I promised to talk about the moon and it is time thatI fulfill the promise. Here is a quote from NASA’sweb site:3

On July 20, 1969, the human race ac-complished its single greatest techno-logical achievement of all time when ahuman first set foot on another celestialbody. Six hours after landing at 4:17p.m. Eastern Daylight Time (with lessthan 30 seconds of fuel remaining), NeilA. Armstrong took the “Small Step”into our greater future when he steppedoff the Lunar Module, named “Eagle,”onto the surface of the Moon, fromwhich he could look up and see Earth inthe heavens as no one had done beforehim.

3http://history.nasa.gov/ap11ann/introduction.htm.

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Even if the style is a bit florid, I quite agree that thiswas the “single greatest technological achievement.”You need only consider what it must have been liketo sit atop massive rockets and to entrust yourselfto the intricate calculation of the celestial mechan-ics involved in performing the various rendezvous.The fact that six out of seven attempts to land onthe moon were totally successful is nothing short ofamazing.

So what did the Apollo computer system looklike [9]. The Apollo Guidance Computer was “fairlycompact” and weighed only 32 kilograms!

The execution of an instruction required two ma-chine cycles—about 24 milliseconds or 83kHz, andthe computer had 36KB words of fixed memory and2KB words of erasable memory. Just for compari-son: I insisted that my boss buy me a modern Pen-tium 4 computer with 256 megabytes of memory;otherwise, it would have been impossible to run cer-tain modern Java-based pedagogical software. Thefixed memory (core rope) was unchangeable once itleft the factory, so the software had to be deliveredmonths before a mission for manufacturing and elec-trical testing, placing a premium on the productionof quality software without hacking. And yet withthis computer system, NASA carried out the “singlegreatest technological achievement of all time!”

I believe that instead investing so much ef-fort in teaching new hi-tech artifacts and in havingour students write large programs with fancy user-interfaces and web sites, we should be emphasiz-ing basics. The history of computing in space of-fers many interesting case studies that can be usedto teach computer science.

• During the first landing on the moon, threerestarts during a 40-second period causedwarning lights to appear. The softwarehad given priority to interrupts that imple-mented counter increment requests, and therendezvous radar caused so many interruptsthat 15% of the system resources were tied up

responding to them. NASA engineers recog-nized to source of the problem and allowed thelanding to continue [9].

• The first flight of the Space Shuttle was can-celed because of a synchronization problembetween the primary computer system and thebackup computer system. It turned out tohave been caused by an inconsistency betweentwo scheduling algorithms that surfaced whenmodifications to software invalidated an as-sumption that a certain process would be ex-ecuted first. If the computer was turned onduring a 15 ms window within each second,the problem would occur. The solution wassimply to turn the computer off and on again[7].

• During the Mars Pathfinder Mission, frequentresets caused loss of data. The problem wasdiagnosised as priority inversion that causeda high-priority data management process notto complete on time. The software was reini-tialized to use priority inheritance [6], and theproblem was solved [4].

• The most expensive bug in history was prob-ably the one that caused the French Ariane 5rocket to explode on its maiden flight. Therocket’s computer system had reused softwarefrom the Ariane 4, but assumptions that hadbeen valid no longer held [5, 2].

These case studies are pedagogically extremelyvaluable, not only for their technical content, butalso because you can discuss issues of testing andreliability that are often glossed over when desktopsoftware is developed.

5 So How Can You Get to theMoon Without Powerpoint?

The presentation for the talk was written in LATEX 2εusing the Prosper style file. The LATEX 2ε sourcefiles were typeset by the VisualTeX (a commeri-cal system) into pdf. The pdf files compressed byWinZip and displayed by Acrobat Reader. All thefiles are, of course, portable.

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References

[1] ACM/IEEE-CS. Computing curricula 2001:Computer science volume. http://www.acm.org/sigcse/cc2001, 2001.

[2] Mordechai Ben-Ari. The bug that destroyed arocket. Journal of Computer Science Educa-tion, 13(2):15–16, 1999.

[3] Florian Coulmas. The Writing Systems of theWorld. Basil Blackwell, Oxford, UK, 1989.

[4] Mike Jones. What really happened onMars Rover Pathfinder. The Risks Digest,19(49), 1997. http://catless.ncl.ac.

uk/Risks/19.49.html.

[5] J. L. Lions. Ariane 5 flight 501 failure: Reportby the inquiry board. http://ravel.esrin.esa.it/docs/esa-x-1819eng.pdf, 1996.

[6] L. Sha, R. Rajkumar, and J. P. Lehoczky. Prior-ity inheritance protocols: An approach to real-

time synchronization. IEEE Transactions onComputers, 39:1175–1185, 1990.

[7] Alfred Spector and David Gifford. The SpaceShuttle primary computer system. Communi-cations ACM, 27(9):874–900, 1984.

[8] Thomas Standage. The Victorian Internet:The Remarkable Story of the Telegraph andthe Nineteenth Century’s On-line Pioneers.Walker Publishing Company, New York, 1998.

[9] James E. Tomayko. Computers inspaceflight: The NASA experience.http://www.hq.nasa.gov/office/pao/

History/computers/Compspace.html,1988.

[10] Robert H Zakon. Hobbes’ Internet time-line. http://www.zakon.org/robert/

internet/timeline, 2002.

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