A Chronology of Digital Computing Machines (to 1952)

Mark Brader

For some time Mark Brader has maintained a chronology of digital computing machines. Resulting from a break in his Internet access, Mark is no longer posting updates regularly to Usenet; instead, I am maintaining this copy on the WWW for him. This page is based on his final posting of the chronology, but has undergone subsequent updating and minor editing (note that the document is deliberately kept in plain text, not HTML).

Please note that Mark's email address has changed again, to <msb@vex.net>.

This page last modified 2002-09-01.

A Chronology of Digital Computing Machines (to 1952)

Last posted June 25, 1997, by Mark Brader
to alt.folklore.computers,comp.misc,soc.history.science
with Message-ID <1997Jun25.194812.28073@sq.com>


As I am leaving SoftQuad (and Usenet, at least for the moment) today,
I thought I would take this opportunity to repost the current version of
the following article which I have been maintaining and which has
appeared several times in these newsgroups.

Followups this time are directed to soc.history.science; if someone else
wants to grab this document and take over maintenance of it, they are
welcome to do so.  As it says at the end, it's in the public domain.


[Canned article follows -- last substantively modified June 8, 2000.]

[This article was prepared using the ISO 8859-1 character set.  If you
 see an i-circumflex in "naquît" and a u-umlaut in "Tübingen",
 that's correct.  If not, be aware that several other words and names here and
 there through the article will also look wrong for you. This should not
 be an issue with the WWW version of this document.]

What was the first computer and who built it?

It turns out that this is more a question of definition than a
question of fact.  The computer, as we now understand the word,
was very much an evolutionary development rather than a simple
invention.  This article traces the sequence of the most important
steps in that development, and in the earlier development of
digital calculators without programmability.  It may help you
to decide for yourself whether you think the first computer was
the ABC, the Z3 (aka V3), the ENIAC, the SSEC, the Manchester
Mark I (aka Baby), the EDSAC, or perhaps yet another machine --
and how to apportion the honor of invention among John Atanasoff,
Charles Babbage, Presper Eckert, John Mauchly, Alan Turing, John
von Neumann, Konrad Zuse, and others.


This article has evolved from an original version that I drafted
in 1988, and has been posted to various Usenet groups several times.
It has been prepared primarily from two sources:

        "Bit by Bit: An Illustrated History of Computers"
         by Stan Augarten
         1984, Ticknor and Fields, New York
         ISBN 0-89919-268-8, 0-89919-302-1 paperback

        "A History of Computing Technology"
         by Michael R. Williams
         1985, Prentice-Hall, Englewood Cliffs, NJ
         ISBN 0-13-389917-9

Either of these books is well worth a trip to the library to read.
(Unfortunately, finding either one in a bookstore today would be an
unlikely proposition.)  Augarten is a journalist; he writes very
readably, but occasionally does not say exactly what he means.
Williams is a computer science professor; his book is superior in
technical depth, and covers additional subject areas including
analog computing and computing in ancient times.

For some material I also consulted the following books.

        "The Dream Machine: Exploring the Computer Age"
         by Jon Palfreman and Doron Swade
         1991, BBC Books, London
         ISBN 0-563-36221-9

The book of the TV series of the same title, which changed to "The
Machine that Changed the World" when it was shown in the US on PBS.
I enjoyed the content but found the typographic design so hideously
mannered as to be distracting.  This book has less technical detail
than the two mentioned above, and a greater emphasis on the impact of
computers on the modern world; a considerable fraction of its length
is about the uninteresting :-) period after the end of this chronology.

        "Portraits in Silicon"
         by Robert Slater
         1987, MIT Press, Cambridge, MA
         ISBN 0-262-69131-0

Articles about, and interviews with, 34 of the people to whom goes
much of the credit for the computer world being the way it is, from
Charles Babbage to Donald Knuth.

        "The Computer Pioneers"
         by David Ritchie
         1986, Simon & Schuster, New York
         ISBN 0-671-52397-X

This one concentrates in the late 1930s and the 1940s, with one chapter
for each of the key inventors or groups of that period.  The author is
a journalist and the book is very readable.

        "The Computer -- My Life"
         Original German version by Konrad Zuse:
                "Der Computer -- mein Lebenswerk"
                 1993, Springer-Verlag, Berlin
                 ISBN 3-540-56292-3
         English translation by Patricia McKenna and J. Andrew Ross
         1993, Springer-Verlag, Berlin and New York
         ISBN 0-387-56453-5 (New York), 3-540-56453-5 (Berlin).

An autobiography.

        "Encyclopedia of Computer Science and Engineering", 2nd ed.
         editor Anthony Ralston, associate Editor Edwin D. Reilly Jr.
         1983, Van Nostrand Reinhold, New York
         ISBN 0-442-24496-7

The title is self-explanatory.

        "The Computer Comes of Age"
         Original French version by R. Moreau:
                "Ainsi naquît l'informatique"
         English translation by J. Howlett
         1984, MIT Press, Cambridge, MA
         ISBN 0-262-36103-2

Concentrating on the period from the mid 1940s to mid 1960s, and
with a noticeably IBMish viewpoint.

        "ENIAC: The Triumphs and Tragedies of the World's First Computer"
         by Scott McCartney
         1999, Walker and Co., New York
         ISBN 0-8027-1348-3

This book has somewhat a wider scope than the title suggests, covering
events in the lives of Presper Eckert and John Mauchly over several decades.
However, it is strictly centered on the two men and tends to "prove" their    
pioneering status by omitting any developments they weren't involved with.    

Two articles from Scientific American were also sources.  One in the
August 1988 issue was about the Atanasoff-Berry machines, and one in the
February 1993 issue of was about Babbage's difference engines and the
modern-day completion of one of them.

Information about the cipher-breaking machines came primarily from
two books:

        "Seizing the Enigma: the Race to Break the German U-Boat Codes,
         by David Kahn
         1991, Houghton Mifflin, Boston
         ISBN 0-395-42739-8

        "Codebreakers: The Inside Story of Bletchley Park"
         edited by F.H. Hinsley and Alan Stripp
         1993, Oxford University Press, Oxford and New York
         ISBN 0-19-820327-6

Kahn is also the author of the monumental cryptological history "The
Codebreakers"; this book is oriented more to a popular readership but
still contains plenty of technical detail.  The second book collects
articles by various individuals involved with the cipher-breaking work;
some are quite technical and others not.

A few items of information come from other sources, not listed individ-
ually here.  One correction about Konrad Zuse came from his son Horst.

And finally, the book

        Faster than Thought
        editor B. V. Bowden
        1953, Pitman, New York and London

provided an interesting early perspective, and the signature quote.


I've tried to mention in this chronology each machine within the
relevant time period that meets the following criteria.  First, it
must use a digital technique to do arithmetic or other logic.  This
eliminates, for instance, the slide rule and the differential analyzer,
while allowing the cipher-breaking machines of the Second World War
to be included.

Second, it must actually do the arithmetic or other work rather than
just assisting the user's memory.  I consider this to eliminate the
abacus as well as, say, Napier's Bones.

Third, to count as being able to do an operation, the machine must do
essentially the whole computation, with little or no assistance from the
user.  You could subtract 16 on a 6-digit Pascaline by adding 999,984,
but this doesn't mean we should say that a Pascaline could subtract.

Fourth, it must work on user-supplied operands.  In 1364, Giovanni
de Dondi completed a clock where chains of various lengths, advancing
in discrete annual steps to represent calendar cycles, computed the
date of Easter; but this still does not qualify.  (For details of
this clock see "Some Outstanding Clocks over Seven Hundred Years,
1250-1950" by H. Alan Lloyd, 1958, Leonard Hill.)

And finally, the machine must have either been technologically
innovative, or else well known and influential.  For certain concepts
of special importance, I have also listed the first time they were
*described*, although they were not implemented at that time.

Where I do not describe the size of a machine, it is generally
suitable for desktop use if it has no memory and is unprogrammable
or if it is a small prototype, but would about fill a small room if
it has memory or significant programmability.

The term "full-scale" is used, in contrast to "prototype", to refer
to a machine with sufficient capacity to do regular useful work.
For the sorts of machines described toward the end of the chronology,
I generally consider them "completed" when they first run a program,
even though they may be subject to further modifications and debugging.
Unfortunately, sources referring to the "completion" of a machine are
not always clear as to exactly what they mean by it.

     A Chronology of Digital Computing Machines (to 1952)

1623.   Wilhelm Schickard (1592-1635), of Tübingen, Württemberg
        (now in Germany), makes his "Calculating Clock".  This is a
6-digit machine that can add and subtract, and indicates overflow
by ringing a bell.  Mounted on the machine is a set of Napier's Rods
(or Bones), a memory aid facilitating multiplications.  The machine
and plans are lost and forgotten in the war that is going on.

The plans will finally be rediscovered in 1935, only to be lost in war
again, and then re-rediscovered in 1956 by the same man!  The machine
will be reconstructed in 1960, and found to be workable.

(Schickard is a friend of the astronomer Kepler.)

(According to an informal communication, Schickard sometimes uses
the device for 7-digit calculations, counting rings of the overflow
bell by putting rings on one of his, uh, personal digits...)

1644-5. Blaise Pascal (1623-62), of Paris, makes his "Pascaline".
        This 5-digit machine uses a different carry mechanism from
Schickard's, with rising and falling weights instead of a direct
gear drive; it can be extended better to support more digits, but
it cannot subtract, and probably is less reliable than Schickard's
simpler method.

Where Schickard's machine is forgotten -- and indeed Pascal is
apparently unaware it ever existed -- Pascal's becomes well known
and establishes the computing machine concept in the intellectual
community.  He makes more machines and sells about 10-15 of them,
some supporting as many as 8 digits.  (Several survive to the
present day.)  Patents being a thing of the future, others also
sell copies of Pascal's machine.

(Pascal is also the inventor of the bus.)

c.1668. Sir Samuel Morland (1625-95), of England, produces a
        non-decimal adding machine, suitable for use with English
money.  Instead of a carry mechanism, it registers carries on
auxiliary dials, from which the user must reenter them as addends.

1674.   Gottfried Wilhelm von Leibniz (1646-1716), of Leipzig,
        designs his "Stepped Reckoner", which is constructed by a
man named Olivier, of Paris.  It uses a movable carriage so that it
can multiply, with operands of up to 5 and 12 digits and a product
of up to 16.  The user has to turn a crank once for each unit in
each digit in the multiplier; a fluted drum translates the turns
into additions.  But the carry mechanism requires user intervention,
and doesn't really work in all cases anyway.

Leibniz's machine doesn't get forgotten, but it does get misplaced
in an attic within a few years -- and will stay there until 1879 when
it will be noticed by a man working on the leaky roof!

(Leibniz, or Leibnitz, is also the co-inventor of calculus.)

1775.   Charles, the third Earl Stanhope, of England, makes a
        successful multiplying calculator similar to Leibniz's.

1770-6. Mathieus Hahn, somewhere in what will be Germany, also makes
        a successful multiplying calculator.

1786.   J. H. Müller, of the Hessian army, conceives the idea of
        what came to be called a "difference engine".  That's a
special-purpose calculator for tabulating values of a polynomial,
given the differences between certain values so that the polynomial
is uniquely specified; it's useful for any function that can be
approximated by a polynomial over suitable intervals.  Müller's
attempt to raise funds fails and the project is forgotten.

1820.   Charles Xavier Thomas de Colmar (1785-1870), of France,
        makes his "Arithmometer", the first mass-produced calculator.
It does multiplication using the same general approach as Leibniz's
calculator; with assistance from the user it can also do division.
It is also the most reliable calculator yet.  Machines of this general
design, large enough to occupy most of a desktop, continue to be sold
for about 90 years.

1822.   Charles Babbage (1792-1871), of London, having reinvented
        the difference engine, begins his (government-funded)
project to build one by constructing a 6-digit calculator using
gear technology similar to that planned for the difference engine.

1832.   Babbage and Joseph Clement produce a prototype segment of
        his difference engine, which operates on 6-digit numbers
and 2nd-order differences (i.e. can tabulate quadratic polynomials).

The complete engine, which would be room-sized, is planned to be
able to operate both on 6th-order differences with numbers of about
20 digits, and on 3rd-order differences with numbers of 30 digits.
Each addition would be done in two phases, the second one taking
care of any carries generated in the first.  The output digits
would be punched into a soft metal plate, from which a plate for a
printing press could be made.

But there are various difficulties, and no more than this prototype
piece is ever assembled.

1834.   George Scheutz, of Stockholm, produces a small difference
        engine in wood, after reading a brief description of
Babbage's project.

1834.   Babbage conceives, and begins to design, his "Analytical
        Engine".  Whether or not this machine, if built, would
constitute a computer depends on exactly how "computer" is being
defined.  One essential feature of present-day computers is absent
from the design: the "stored-program" concept, which is necessary
for implementing a compiler.  The program would have been in
read-only memory, specifically in the form of punch cards.  (In
this chronology, such machines will be called "programmable cal-

Babbage continues to work on the design for years, though after
about 1840 the changes are minor.  The machine would operate on
40-digit numbers; the "mill" (CPU) would have 2 main accumulators
and some auxiliary ones for specific purposes, while the "store"
(memory) would hold perhaps 100 more numbers.  There would be
several punch card readers, for both programs and data; the cards
would be chained and the motion of each chain could be reversed.
The machine would be able to perform conditional jumps.  There
would also be a form of microcoding: the meaning of instructions
would depend on the positioning of metal studs in a slotted
barrel, called the "control barrel".

The machine would do an addition in 3 seconds and a multiplication
or division in 2-4 minutes.

1842.   Babbage's difference engine project is officially canceled.
        (The cost overruns have been considerable, and Babbage is
spending too much time on redesigning the Analytical Engine.)

1843.   Scheutz and his son Edvard Scheutz produce a 3rd-order
        difference engine with printer, and the Swedish government
agrees to fund their next development.

1847-9. Babbage designs an improved, simpler difference engine,
        which will operate on 7th-order differences and 31-digit
numbers, but nobody is interested in paying to have it built.

(In 1989-91, however, a team at London's Science Museum will do
just that.  They will use components of modern construction, but
with tolerances no better than Clement could have provided... and,
after a bit of tinkering and detail-debugging, they will find that
the machine does indeed work.)

1853.   To Babbage's delight, the Scheutzes complete the first
        full-scale difference engine, which they call a Tabul-
ating Machine.  It operates on 15-digit numbers and 4th-order
differences, and produces printed output as Babbage's would have.
A second machine is later built to the same design by the firm
of Bryan Donkin of London.

1858.   The first Tabulating Machine is bought by the Dudley
        Observatory in Albany, New York, and the second one by
the British government.  The Albany machine is used to produce
a set of astronomical tables; but the observatory's director is
then fired for this extravagant purchase, and the machine is
never seriously used again, eventually ending up in a museum.
(The second machine, however, will have a long and useful life.)

1871.   Babbage produces a prototype section of the Analytical
        Engine's mill and printer.

1878.   Ramon Verea, living in New York City, invents a calculator
        with an internal multiplication table; this is much faster
than the shifting carriage or other digital methods.  He isn't
interested in putting it into production; he just wants to show that
a Spaniard can invent as well as an American.

1879.   A committee investigates the feasibility of completing the
        Analytical Engine and concludes that it is impossible now
that Babbage is dead.  The project is then largely forgotten and is
unknown to most of the people mentioned in the last part of this
chronology -- though Howard Aiken is an exception.

1885.   A multiplying calculator more compact than the Arithmometer
        enters mass production.  The design is the independent, and
more or less simultaneous, invention of Frank S. Baldwin, of the
United States, and T. Odhner, a Swede living in Russia.  The fluted
drums are replaced by a "variable-toothed gear" design: a disk with
radial pegs that can be made to protrude or retract from it.

1886.   Dorr E. Felt (1862-1930), of Chicago, makes his "Comptometer".
        This is the first calculator where the operands are entered
merely by pressing keys rather than having to be, for example, dialed
in.  It is feasible because of Felt's invention of a carry mechanism
fast enough to act while the keys return from being pressed.

1889.   Felt invents the first printing desk calculator.

1890.   US Census results are tabulated for the first time with sig-
        nificant mechanical aid: the punch card tabulators of Herman
Hollerith (1860-1929) of MIT, Cambridge, MA.  This is the start of
the punch card industry.  The cost of the census tabulation is 98%
*higher* than the previous one, in part because of the temptation to
use the machines to the fullest and tabulate more data than formerly
possible, but the tabulation is completed in a much shorter time.
Another precedent is that the cards are read electrically.

(Contrary to popular impression and to earlier versions of this
chronology, Hollerith's cards of 1890 are not the same size as
US paper money of the time; they are much smaller.  Other sizes of
punch cards will also appear within a few years.)

1892.   William S. Burroughs (1857-98), of St. Louis, invents a
        machine similar to Felt's but more robust, and this is the
one that really starts the office calculator industry.

(This machine is still hand powered, but it won't be many years
before electric calculators appear.)

1906.   Henry Babbage, Charles's son, with the help of the firm of
        R. W. Munro, completes the mill of his father's Analytical
Engine, just to show that it would have worked.  It does.  The
complete machine is never produced.

1919.   W. H. Eccles and F. W. Jordan publish the first flip-flop
        circuit design.

c.1920. Eugène Carissan of France constructs a machine for factoring
        whole numbers, based on 14 rotating metal rings studded with pegs.

1926.   Derrick Henry Lehmer, at Berkeley, CA, constructs a machine for
        factoring whole numbers, based on 19 bicycle chains.  A later
machine will use punched tape -- not paper tape, but film stock.

(Lehmer is the son of mathmatician Derrick Norman Lehmer.)

1931-2. E. Wynn-Williams, at Cambridge, England, uses thyratron
        tubes to construct a binary digital counter for use in
connection with physics experiments.

1932.   Lehmer adds an optical reader to his punched-film factoring
        machine.  It is now capable of 5,000 operations per second.

1935.   International Business Machines introduces the "IBM 601",
        a punch card machine with an arithmetic unit based on relays
and capable of doing a multiplication in 1 second.  The machine
becomes important both in scientific and commercial computation,
and about 1,500 of them are eventually made.

Jun 1937.  Konrad Zuse (1910-95) of Berlin writes in his diary a
        synopsis of the stored-program concept:  "Die Operationen
folgen einem Plan ähnlich einem Rechenplan.  Mit Ausgangsbedingungen
und Resultat.  Dementsprechend Speicherplan.  Jedoch kann der
Speicher- oder Arbeitsplan sich aus den vorhergehenden Operationen
ergeben (z.B. die Nummern der Speicherzellen) und sich so aus sich
selbst aufbauen (vgl. 'Keimzelle')."  That is, "The operations follow
a plan similar to a computing plan.  With initial conditions and
result.  Accordingly, a storage plan.  However, the storage or work
plan can still result from the preceding operations (e.g. the
numbers in the storage cells) and in this way be built from itself
(cf. 'germ cell')."

Nov 1937.  George Stibitz (c.1904 - 1995) of the Bell Telephone Labor-
        atories (Bell Labs), New York City, constructs on his kitchen
table the "K-Model": a demonstration 1-bit binary adder using relays.

1937.   Alan M. Turing (1912-54), of Cambridge University, England,
        publishes a paper on "computable numbers".  This paper solves
a mathematical problem, but the solution is achieved by reasoning
(as a mathematical device) about the theoretical simplified computer
known today as a Turing machine.

Nov 1938.  Marian Rejewsky (a man, 1905-80) and his group, working
        for Poland's Biuro Szyfrów (Cipher Office), complete the first
"bomba", a machine using electromechanical digital logic for trying
out combinations of letters to solve the Germans' Enigma cipher.
The Enigma machine uses a series of disks ("rotors") with sets of
26 contacts wired so as to permute and repermute the alphabet; the
sequence of rotors and their initial settings are changed from time
to time, forming a key.

The bomba contains its own set of rotors like the Enigma's, and its
function is to determine, through a combination of logic with an
exhaustive search of rotor positions, whether a particular short
piece of guessed plaintext and a particular piece of encrypted text
could correspond.  If the plaintext was correctly guessed, then the
key can be derived from the bomba results, and not only the rest of
that message, but all others using the same key can then be decrypted.
And if it wasn't, then the same guess will be tried against other

(But the next month, the Germans will add a selection of additional
rotors to their Enigma machines.  The Poles, not having the resources
to build more bomby, in July 1939 will turn over all their discoveries
to the British and the French.)

1938.   Claude E. Shannon (1916-2001) publishes a paper on the
        implementation of symbolic logic using relays.

1938.   Helmut Schreyer, of Berlin, designs logic circuitry based on
        a combination of vacuum tubes and neon lamps.  (By 1940 he
will have produced a 10-bit adder and a prototype memory unit.)

1938.   Zuse, with some assistance from Schreyer, completes a
        prototype electromechanical binary programmable calculator,
called the "V1" at the time but retroactively renamed "Z1" after the
war.  It works with floating point numbers having a 7-bit exponent,
16-bit mantissa, and a sign bit.  The memory uses sliding metal parts
to store 16 such numbers, and works well; but the arithmetic unit,
using secondhand relays and stepping switches, is less successful.

The program is read from punched tape.  Like Lehmer, Zuse uses film
rather than paper for his tape; specifically, discarded 35 mm movie
film.  Data values can be entered from a numeric keyboard, and
outputs are displayed on electric lamps.

Nov 1939.  John V. Atanasoff (1903-95) and graduate student Clifford
        Berry (1918-63), of Iowa State College (now the Iowa State
University), Ames, Iowa, complete a prototype 25-bit adder.  This
is the first machine to calculate using vacuum tubes.  To store the
operands, it has 2 25-bit words of memory in the form of capacitors
(with refresh circuits using more vacuum tubes -- the first regen-
erative memory) mounted one word on each side of a revolving disk.
There is no input device; the user enters the operands directly into
memory, by tapping the appropriate capacitors with a wire!

Nov 1939.  At Bell Labs, Samuel Williams and Stibitz complete a
        calculator which can operate on complex numbers, and give it
the imaginative name of the "Complex Number Calculator"; it is later
known as the "Model I Relay Calculator".  It uses telephone switching
parts for logic: 450 relays and 10 crossbar switches.  Numbers are
represented in "plus 3 BCD"; that is, for each decimal digit, 0 is
represented by binary 0011, 1 by 0100, and so on up to 1100 for 9;
this scheme requires fewer relays than straight BCD.

Rather than requiring users to come to the machine to use it, the
calculator is provided with three remote keyboards, at various
places in the building, in the form of teletypes.  Only one can be
used at a time, and the output is automatically displayed on the
same one.

1939.   Zuse and Schreyer begin work on the "V2" (later "Z2"),
        which will marry the Z1's existing mechanical memory unit to
a new arithmetic unit using relay logic.  The project is interrupted
for a year when Zuse is drafted.

Early 1940.  Turing and Gordon Welchman (1906-85), working for
        the British government codebreaking department deceptively
named the Government Code and Cypher School, at Bletchley Park,
Bletchley, England, successively improve the design of the bomba
by adding further logic circuits.  These greatly reduce the number
of false solutions.  With quantity production of these machines, now
called bombes, the full-scale breaking of Enigma ciphers becomes a
practical proposition.

(After the US joins the war, they will make and use them too.
Improvements on the machines will continue, as the Germans also
improve the cipher.)

1940.   Zuse is released from the army and completes the Z2.
        It works better than the Z1, but isn't reliable enough.
(Later he is drafted again, and released again.)

Sep 1940.  Stibitz, attending a mathematical conference in Hanover,
        NH, to present a paper on the Complex Number Calculator,
demonstrates operation of the machine from a remote location by
teletype connection.

Summer 1941. Atanasoff and Berry complete a special-purpose calcu-
        lator for solving systems of simultaneous linear equations,
later called the "ABC" ("Atanasoff-Berry Computer").  This uses the
same regenerative capacitor memory as their prototype, but with 60
50-bit words of it, mounted on two revolving drums.  The clock speed
is 60 Hz, and an addition takes 1 second.  (For the purposes of this
calculator, multiplication is not required.)  There are circuits to
convert between binary and decimal for input and output; the machine
includes several hundred vacuum tubes altogether.

For secondary memory the ABC uses punch cards, moved around by the
user.  The holes are not actually punched in the cards, but burned
by an electric spark.  The card system is a partial failure; its
error rate of 0.001% is too high to solve large systems of equations.

(Atanasoff will leave Iowa State after the US enters the war, and
this will end his work on digital computing machines.  The ABC will
largely forgotten within a few years, and dismantled in 1946 when
the storage space is needed.)

Dec 1941.  Now working with limited backing from the DVL (German Aero-
        nautical Research Institute), Zuse completes the "V3" (later
"Z3"): the first operational programmable calculator.  It works with
floating point numbers having a 7-bit exponent, 14-bit mantissa
(with a "1" bit automatically prefixed unless the number is 0),
and a sign bit.  The memory uses relays; with a capacity of 64 words,
it needs over 1,400 of them.  There are 1,200 more relays in the
arithmetic and control units.  The machine is the size of a closet.

The program, input, and output are implemented as described above for
the Z1.  Conditional jumps are not available.  The machine can do 3-4
additions per second, and takes 3-5 seconds for a multiplication.
Zuse considers the machine a prototype; it doesn't have enough memory
to be much use for the equation-solving problems that the DVL was
mostly interested in.

(In 1943, an air raid will destroy Zuse's workshop, and the Z3 with
it, as well as his home nearby.  A replica Z3 will be built in 1960
for the Deutsches Museum in Munich.  And in 1967, the Patent Office
of West Germany will finally rule on Zuse's 1941 application for a
patent on the Z3, rejecting it "mangels Erfindungshöhe": "for an
insufficient degree of invention"!)

1942.   Zuse completes the S1, the first digital machine for process
        control.  Attached sensors measure the profile of the wing of
a flying bomb under construction; the readings are converted to dig-
ital and computations are run to determine how much the wing deviates
from the ideal shape and needs to be adjusted.  (This is cheaper than
making it accurately in the first place.)  The machine contains 800
relays; the program is literally wired in, each instruction being read
by advancing a set of stepping switches.

Jan 1943.  Howard H. Aiken (1900-73) and his IBM-backed team at
        Harvard University, Cambridge, MA, complete the "ASCC Mark I"
("Automatic Sequence-Controlled Calculator Mark I"), also called the
"Harvard Mark I".  This electromechanical machine is the first pro-
grammable calculator to be widely known:  Aiken is to Zuse as Pascal
to Schickard.

The machine is 51 feet long, weighs 5 tons, and incorporates 750,000
parts.  It includes 72 accumulators, each incorporating its own arith-
metic unit as well as a mechanical register with a capacity of 23
digits plus sign.  (See the ENIAC entry, below, for a more detailed
description of such an architecture.)  The arithmetic is fixed-point,
with a plugboard setting determining the number of decimal places.
I/O facilities include card readers, a card punch, paper tape readers,
and typewriters.  There are 60 sets of rotary switches, each of which
can be used as a constant register -- sort of a mechanical read-only
memory.  An addition takes 1/3 second, and a multiplication, 1 second.

The program is read from one paper tape; data can be read from the
other tapes, or the card readers, or from the constant registers.

Conditional jumps are not available.  However, in later years the
machine is modified to support multiple paper tape readers for the
program, with the transfer from one to another being conditional,
sort of like a conditional subroutine call.  Another addition allows
the provision of plugboard-wired subroutines callable from the tape.

Apr 1943.  Max Newman, Wynn-Williams, and their team at Bletchley
        Park, complete the "Heath Robinson".  This is a prototype
machine for breaking the new German ciphers collectively codenamed
the "Fish" ciphers, which are based on bit-level manipulations rather
than permutations of the alphabet.  The machine uses a combination
of electronics and relay logic.  It reads data optically at 2,000
characters per second from 2 closed loops of paper tape, each
typically about 1,000 characters long.

(Newman had taught Turing at Cambridge, and had been the first person
to see a draft of Turing's 1937 paper.  Heath Robinson is the name of
a British cartoonist known for drawings of comical machines, like
the American Rube Goldberg.  Two later machines in the series will be
named for London stores with "Robinson" in their names!)

Apr 1943.  John W. Mauchly (pronounced Mawkly; 1907-80), J. Presper
        Eckert (1919-95), and John Brainerd at the Moore School of
Electrical Engineering, of the University of Pennsylvania, Phila-
delphia, write a "Report on an Electronic Diff. Analyzer" for the
US Army's Ballistics Research Lab.  The abbreviation "Diff." is
intended to reflect the fact that the proposed machine, eventually
named the ENIAC ("Electronic Numerator, Integrator, Analyzer, and
Computer"; some sources omit "Analyzer" or have "Calculator" as the last
word), is to use *differences* to compute digitally the same results
that a *differential* analyzer would compute by analog means.  The BRL,
which has a great interest in calculating shell trajectories to produce
gun aiming tables, accepts the proposal and work on the ENIAC begins in

Sep 1943.  Williams and Stibitz complete the "Relay Interpolator",
        later called the "Model II Relay Calculator".  This is a
programmable calculator; again, the program and data are read from
paper tapes.  An innovative feature is that, for greater reliability,
numbers are represented in a biquinary format using 7 relays for
each digit, of which exactly 2 should be "on": 01 00001 for 0,
01 00010 for 1, and so on up to 10 10000 for 9.

(Some of the later machines in this series will use the biquinary
notation for the digits of floating-point numbers.)

Dec 1943.  Tommy Flowers (1905-98) and his team at Bletchley Park
	complete the first "Colossus".  This full-scale successor to
the "Robinson" series machines is entirely electronic, incorporating
2,400 vacuum tubes for logic.  It has 5 paper tape loop readers,
each working at 5,000 characters per second.

(10 Colossi will eventually be built, then destroyed after the war
to maintain secrecy.  Turing also has an important role at Bletchley
Park, but does not work directly on the machines.  In the 1990s
Bletchley Park will become a museum, and in 1996 a replica Colossus
will be completed there.)

1944-5. Zuse almost completes his first full-scale machine, the "V4"
        (later "Z4"), which resembles his earlier designs.  Its
memory reverts to the Z1's mechanical design, storing 1,000 words of
32 bits in less then a cubic meter; the equivalent in relays would
have filled a large room.

As the war begins to go very badly for Germany, Zuse's work suffers
major disruptions.  The Z4 is moved three times within Berlin, then
to Göttingen, and finally to the Bavarian village of Hinterstein
where it is hidden.  Here it survives the war, but the Allies don't
understand what it is, and nobody in Germany is in a position to pay
Zuse for more work.

1945.   Zuse invents a programming language called Plankalkül.

Jun 1945.  John von Neumann (1903-57), having joined the ENIAC
        team, drafts a report describing the future computer
eventually built as the "EDVAC" ("Electronic Discrete Variable
Automatic Computer" (!)); this is the first detailed description
of the design of a stored-program computer, and gives rise to the
term "von Neumann computer".

The first draft of the report fails to credit other team members
such as Eckert and Mauchly; when this version becomes widely
circulated, von Neumann gets somewhat too much credit for the
design.  The final version corrects the oversight, but too late.

(Von Neumann, also noted for his mental calculating ability, is
the only one of the principal computer pioneers in the US familiar
with Turing's 1937 paper.)

Nov 1945.  Mauchly and Eckert and their team at the Moore School
        complete the ENIAC.  It's too late for the war, and the
total cost of $486,800 far exceeds the original budget of $150,000
(problems that Eckert and Mauchly will face again on later projects),
but it works.

The ENIAC's architecture resembles that of the Harvard Mark I, but
its components are entirely electronic, incorporating 17,468 vacuum
tubes and more than 80,000 other components.  The machine weighs 30
tons, covers about 1,000 square feet of floor, and consumes somewhere
between 130 and 174 kilowatts of electricity (sources differ).  Many
of the modules are made to plug into the mainframe, to shorten the
repair time when a tube or other component fails.  The cost and
downtime are further reduced by using circuits designed to work even
if the components are off-specification, and wire of the type least
preferred by hungry mice in experiments.

The machine incorporates 20 accumulators (the original plan was for 4).
The accumulators and other units are all connected by several data
buses, and a set of "program lines" for synchronization.  Each accum-
ulator stores a 10-digit number, using 10 bits to represent each digit,
plus a sign bit, and also incorporates circuits to add a number from
a bus ("digit trunk") to the stored number, and to transmit the stored
number or its complement to a bus.

A separate unit can perform multiplication (in about 3 milliseconds),
while another does division and square roots; the inputs and outputs
for both these units use the buses.  There are constant registers, as
on the Harvard Mark I: 104 12-digit registers forming an array called
the "function table".  100 of these registers are directly addressable
by a 2-digit number from a bus (the others are used for interpolations).
Finally, a card reader is available to input data values, and there
is a card punch for output.

The program is set up on a plugboard -- this is considered reasonable
since the same or similar program would generally be used for weeks
at a time.  For example, connecting certain sockets would cause
accumulator 1 to transmit its contents onto data bus 1 when a pulse
arrived on program line 1; meanwhile several accumulators could be
adding the value from that data bus to their stored value, while
others could be working independently.  The program lines are pulsed
under the control of a master unit, which can perform iterations.

The ENIAC's clock speed is 100 kHz.

Mauchly and Eckert apply for a patent.  The university disputes this
at first, but they settle.  The patent is finally granted in 1964,
but is overturned in 1973, in part because of the previous work by
Atanasoff, whom Mauchly had visited in June 1941.

Feb 1946.  The ENIAC is revealed to the public.  A panel of lights is
        added to help show reporters how fast the machine is and what
it is doing; and apparently Hollywood takes note.

Jul-Aug 1946. The Moore School gives a course on "Theory and Techniques
        for Design of Electronic Computers"; lectures are given by
Eckert, Mauchly, Stibitz, von Neumann, and Aiken among others.  The
course leads to several projects being started, among them the EDSAC.

Jul 1947.  Aiken and his team complete the "Harvard Mark II", a large
        programmable calculator using relays both for its 50 floating-
point registers and for the arithmetic unit, 13,000 of them in all.

Sep 1947.  A moth (?-1947) makes the mistake of flying into the Harvard
        Mark II.  A whimsical technician makes the logbook entry "first
actual case of bug being found", and annotates it by taping down the
remains of the moth.

(The term "bug" was of course already in use; that's why it's funny.
Grace Murray Hopper (1906-92), a programmer on the machine, will tell
the story so many times in later years that people will come to think
she found the moth herself.)

Oct 1947.  Freddie C. Williams (1911-77) and Thomas Kilburn (1921-),
        working under Newman at Manchester University, complete a new
type of digital memory (possibly from an original suggestion by Presper
Eckert), which comes to be called the Williams tube or CRT memory.
It uses the residual charges left on the screen of a CRT after the
electron beam has been fired at it; the bits are read by firing
another beam through them and reading the voltage at an electrode
beyond the screen, then rewriting.  The technique is a little
unreliable, but is fast, and also relatively cheap because it can
use existing CRT designs; and it is much more compact than any other
memory existing at the time.  A further advantage is that if the CRT
face is exposed to view, the values in the memory are visible!

1947.   Frederick Viehe (?-1960), of Los Angeles, applies for a patent
        on an invention which is to use magnetic core memory.

1947.   Aiken predicts that the United States will need a total of six
        electronic digital computers.

c.1947. The magnetic drum memory is independently invented by several
        people, and the first examples are constructed.

(As noted below, some early machines will use drums as main memory
rather than secondary memory.)

Jan 1948.  Wallace Eckert (1902-71, no relation to Presper Eckert)
        of IBM, with his team, completes the "SSEC" ("Selective
Sequence Electronic Calculator").  This technological hybrid has
8 vacuum tube registers, 150 words of relay memory, and 66 paper
tape loops storing a total of 20,000 words.  The word size is
20 digits, stored in BCD in the registers.

As with the Harvard Mark I in its later form, the machine can be
switched to read instructions from any of the paper tapes.  There
is also some use of plugboards in its programming.  But it can
also cache some instructions in memory and read them from there;
thus, in effect, it can operate either as a stored-program computer
(with a very small program memory) or not.  Because it can do this,
IBM's point of view is that this is the first computer.

Jun 1948.  Williams, Kilburn, and their team complete a prototype
        computer.  This is the first machine that everyone would
call a computer, because it's the first with a true stored-program
capability.  At this point it has no formal name, though one paper
calls it the "Small-Scale Experimental Machine"; later the machine
will become known as the "Manchester Mark I", while its initial
form at this date will be nicknamed the "Baby".

The machine's main memory of 32 32-bit words occupies a single
Williams tube.  (There are others on the machine, but less densely
used: one contains only an accumulator.)

The machine's programs are initially entered in binary on a keyboard,
and the output is read in binary from the face of another Williams
tube.  Later Turing joins the team (see also the "Pilot ACE", below)
and devises a primitive form of assembly language, one of several
developed at about the same time in different places.

(In the 1990s a replica of the Baby is to be constructed, with
completion scheduled for the 50th anniversary year of 1998.)

Sep 1948.  The ENIAC is improved, using ideas from Richard F. Clipper
        of the BRL and Nicholas Metropolis of Los Alamos.  Each program
line is permanently wired for a different operation, and a new converter
unit allows them to be addressed by a program, the way the function
table can -- thus implementing, in effect, opcodes.  With this change,
the program can now be entered via the *function table*.

(This conversion will sometimes be described as making the ENIAC into a
stored-program computer, but the program memory is still read-only.
However, setting up a program now takes a matter of hours, rather than
days as before.  The ENIAC will also acquire a magnetic core memory in
1952, but will survive only until 1955.)

Fall 1948. IBM introduces the "IBM 604", a programmable calculator
        and card punch using vacuum tubes.  It can read a card,
perform up to 60 arithmetic operations in 80 milliseconds, and punch
the results on the same card.  The programming is by plugboard.

All machines first mentioned in the chronology from here on are
stored-program computers.

1949-51. Jay W. Forrester and his team at MIT construct the
        "Whirlwind" for the US Navy's Office of Research and
Inventions.  The vague date is because its advance to full-time
operational status is gradual.  Its original form has 3,300 tubes
and 8,900 crystal diodes.  It occupies 2,500 square feet of floor.
Its 2,048 16-bit words of CRT memory use up $32,000 worth of tubes
each month.  There is also a graphical I/O device consisting of a
CRT (only one dot can be displayed at a time) and a light pen.
This allows the machine to be used for air traffic control.

The Whirlwind is the first computer designed for real-time work;
it can do 500,000 additions or 50,000 multiplications per second.

Spring 1949. Forrester conceives the idea of magnetic core memory as
        it is to become commonly used, with a grid of wires used to
address the cores.  The first practical form, in 1952-53, will replace
the Whirlwind's CRT memory and render obsolete all types of main
memory then existing.

April 1949. The Manchester Mark I, no longer the Baby as its main
        memory has been upgraded to 128 40-bit words (on two CRTs),
acquires a secondary memory in the form of a magnetic drum holding
a further 1,024 words.  Also at about this time, two index registers
are added to the machine.

(The index register's contents are added, not to the address taken
from an instruction, but to the entire instruction, thus potentially
changing the opcode!  Calling Mel...)

May 1949.  Maurice Wilkes (1913-) and his team at Cambridge Uni-
        versity complete the "EDSAC" ("Electronic Delay Storage
Automatic Computer"), which is closely based on the EDVAC design
report from von Neumann's group -- Wilkes had attended the 1946
Moore School course.  The project is supported both financially
and with technical personnel from J. Lyons & Co. Ltd., a large
British firm in the food and restaurant business.

This is the first operational full-scale stored-program computer,
and is therefore the final candidate for the title of "the first

Its main memory is of a type that had existed for some years, but
had not been used for a computing machine: the "ultrasonic delay
line" memory.  It had been invented originally by William Shockley
of Bell Labs (also one of the co-inventors of the transistor, in
1948), and improved by Presper Eckert for use with radar systems.
It works by repeatedly converting from the usual electrical data
pulses to ultrasonic pulses directed along, typically, the length
of a tank of mercury; on arrival at the other end, the pulses are
converted back to electrical form.  The memory must be maintained
at a particular temperature, and only the few bits currently in
electrical form are accessible.  In the EDSAC, 16 tanks of mercury
give a total of 256 35-bit words (or 512 17-bit words).

The clock speed of the EDSAC is 500 kHz; most instructions take
about 1.5 ms to execute.  Its I/O is by paper tape, and a set of
constant registers is provided for booting.

The software eventually supports the concept of relocatable proce-
dures with addresses bound at load time.

Aug 1949.  Presper Eckert and Mauchly, having formed their own company,
        complete the "BINAC" ("Binary Automatic Computer") for the
US Air Force.  Designed as a first step to in-flight computers, this
has dual (redundant) processors each with 700 tubes and 512 31-bit
words of memory.  Each processor occupies only 4 square feet of floor
space and can do 3,500 additions or 1,000 multiplications per second.

The designers are thinking mostly of their forthcoming "UNIVAC"
("Universal Automatic Computer") and don't spend much time making
the BINAC as reliable as it should be, but the tandem processors
compensate somewhat.

Sep 1949.  Aiken's team completes the "Harvard Mark III".  This
        computer has separate magnetic drum memories for data and
instructions.  Only some of the data drums can be addressed by
the CPU; the others serve as secondary memory.  The total memory
capacity is 4,000 instructions, 350 16-bit words in the main data
drums, and 4,000 words more in the secondary memory.  The machine
contains over 5,000 vacuum tubes and 2,000 relays, and can do about
80 multiplications per second.

May 1950.  A group at the National Physical Laboratory, Teddington,
        England, complete the "Pilot ACE" (pilot project for an
"Automatic Computing Engine").  This had been largely designed by
Turing when he was there in 1945-47; he had left and gone to Manches-
ter because the designs were not being implemented.  The main memory
of this computer is in the form of 200 separate ultrasonic delay
lines, thus allowing better addressability than other ultrasonic-
based machines.  An additional group of short delay lines serve as
registers, each of which performs a particular operation automatic-
ally on a number directed to it.  Most operations then consist simply
of routing a number, or a counted stream of numbers, from one delay
line to another.  Punch cards are used for input and output; a drum
will be added later for secondary memory.

(A successor to this machine will be named "DEUCE".)

May 1950.  A group at the US National Bureau of Standards, Washington,
        which had found itself unable to wait for commercial computers
to appear, completes "SEAC" (Standards Eastern Automatic Computer").
The design was kept simple for the sake of rapid implementation.
To keep the number of vacuum tubes down, 12,000 of the new germanium
diodes are used.  The ultrasonic delay line memory holds 512 45-bit

July 1950. SEAC's western counterpart "SWAC", in Los Angeles, is
        completed and becomes the fastest computer in the world.
It has Williams tube memory, which has problems because the tubes'
phosphor layers were contaminated by lint at the former mattress
factory where the tubes were made, and only 256 37-bit words of
main memory are operable.  But it can do an addition in 64 micro-
seconds, and a drum is added later to augment the memory.

1950.   Zuse's Z4 is finally completed and goes into service at
        ETH (Federal Polytechnical Institute) in Zurich, Switzerland.
The design is modified so that it can do conditional jumps.  The
machine also implements a form of instruction pipelining, with the
program tape being read 2 instructions ahead and various optimiz-
ations performed automatically.

The Z4 remains in use for 5 years at ETH and 5 more in France, and
Zuse soon begins making his machines commercially.  He eventually
sells some 300 machines before being bought out by Siemens.

1950.   Douglas Hartree (the leading expert in the country on the
        specialized computing machines called differential analyzers)
gives his professional opinion to Ferranti Ltd., of Manchester:
as the 3 existing computer projects will suffice to handle all the
calculations that will ever be needed in England, Ferranti would be
well advised to drop the idea of making computers for commercial sale.

Feb 1951.  A rather more optimistic Ferranti Ltd. completes the first
        commercial computer.  This is yet another "Mark I", but is
also known as the "Manchester Mark II", "MUDC", "MUEDC", and "MADAM"!
It has 256 40-bit words of main memory and 16K words of drum, and
includes 8 index registers (they work the same way as on the Manchester
Mark I, which this machine was derived from).  An eventual total of 8
of these machines are sold.

Mar 1951.  Presper Eckert and Mauchly, having sold their company to
        Remington Rand, complete the first "UNIVAC", which is the
first US commercial computer.  (The US census department is the first
customer.)  It has 1,000 12-digit words of ultrasonic delay line memory
and can do 8,333 additions or 555 multiplications per second; it con-
tains 5,000 tubes and covers 200 square feet of floor.  For secondary
memory it uses 1/2 inch magnetic tapes of nickel-coated bronze, which
store 128 characters per inch; 10,000 characters can be read per second.

Fall 1951.  The Lyons company receives its reward for supporting the
        EDSAC, as T. Raymond Thompson, John Simmons, and their team
complete the "LEO I" ("Lyons Electronic Office I"), which is modeled
closely after the EDSAC.  Its ultrasonic memory is 4 times as large,
and avoids the usual temperature dependency by using one delay line
as a master and synchronizing the others to it instead of to a clock.

The Lyons company wants the LEO I for its own use -- payroll, inven-
tory, and so on; it is the first computer used for commercial calcul-
ations.  But other companies now turn out to be interested in the LEO,
and Lyons will soon find itself in the computer manufacturing business
as well.

1951.   Grace Murray Hopper, now of Remington Rand, invents the
        modern concept of the compiler.

1952.   The EDVAC is finally completed.  It has 4,000 tubes, 10,000
        crystal diodes, and 1,024 44-bit words of ultrasonic memory.
Its clock speed is 1 MHz.

1952.   The IBM "Defense Calculator", later renamed the "701", the
        first IBM computer unless you count the SSEC, enters
production at Poughkeepsie, New York.  (The first one is delivered
in March 1953; 19 are sold altogether.  The machine is available
with 2,048 or 4,096 36-bit words of CRT memory; it does 2,200 multi-
plications per second.)

(IBM stayed out of the computer market for some time because its
president, Thomas Watson Sr., didn't want the company competing
against its own business machines.  His son and eventual successor,
Thomas Jr., disagreed, and realized that if it was the US *military*
that wanted to buy a computer, Thomas Sr. would not say no to them.)

1952.   Grace Murray Hopper implements the first compiler, the "A-0".
        (But as with "first computer", this is a somewhat arbitrary


A few things have happened since then, too, but this margin is too

Mark Brader           \"The age of chivalry is gone. That of sophisters, econ-
formerly msb@sq.com,   \ omists, and calculators, has succeeded; and the glory
SoftQuad Inc.,Toronto   \ of Europe is extinguished for ever." -- Burke, 1792

This article is in the public domain.

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