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 V3 (aka Z3), the ENIAC, the SSEC, the Manchester Mark I, 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 four books.
The Dream Machine: Exploring the Computer Age
by Jon Palfreman and Doron Swade
BBC Books, London, 1991
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 on 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 Comes of Age / Ainsi naquit l'informatique
by R. Moreau, English translation by J. Howlett
1981, translated 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.
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 August 1988 issue of Scientific American contained an article about the Atanasoff-Berry machines. There is also a book by Clark Mollenhoff about them, some information from which was forwarded to me by email. And the February 1993 issue of Scientific American contained an article about Babbage's difference engines and the modern-day completion of one of them.
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 do arithmetic digitally; this eliminates, for instance, the slide rule. Second, it must actually do arithmetic rather than just assisting the user's memory; I consider this to eliminate the abacus as well as, say, Napier's Bones. Third, it 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 999984, 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 that used chains of various lengths to represent calendar cycles and compute the date of Easter, but this does not qualify even if the chains advanced in discrete "digital" steps (I haven't seen a description detailed enough to say whether they did).
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 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.
The names Tuebingen, Wuerttemberg, and Mueller should have an umlauted "u" in place of the "ue" used in this ASCII text.
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...)
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.)
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.)
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.
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- culators".)
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.
(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.)
(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.)
(This machine is still hand powered, but it won't be many years before electric calculators appear.)
Alan M. Turing (1912-1954), 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.
Konrad Zuse (1910-) of Berlin, with some assistance from Helmut Schreyer, completes a prototype mechanical binary programmable calculator, originally called the "V1" 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 is less successful.
The program is read from punched tape -- not paper tape, but discarded 35 mm movie film. Data values can be entered from a numeric keyboard, and outputs are displayed on electric lamps.
(Zuse is a friend of Wernher von Braun, who will later develop the other "V2", and after that, play a key role in the US space program.)
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. In September 1940, a teletype is set up at a mathematical conference in Hanover, New Hampshire, with a connection to New York, and those attending the conference can use the machine remotely.
For secondary memory it uses punch cards, moved around by the user. The holes are not actually punched in the cards, but burned. The punch card system's error rate is never reduced beyond 0.001%, and this isn't really good enough.
(Atanasoff will leave Iowa State after the US enters the war, and this will end his work on digital computing machines.)
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. It is a marginal decision whether to call the Z3 a prototype; with its small memory it is certainly not very useful on the equation- solving problems that the DVL was mostly interested in.
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.
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.
(Turing was a student of Newman's.)
(The secrecy that surrounded this machine and its successors at Bletchley Park will still be partially in effect at the time of writing, hence the vague description. Newman knew Turing from 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!)
(Some of the later machines in this series will use the biquinary notation for the digits of floating-point numbers.)
(10 Colossi will eventually be built. Turing also has an important role at Bletchley Park, but does not work directly on the machines.)
As the war begins to go very badly for Germany, Zuse's work is dis- rupted several times, and then abandoned for the duration. An air raid had destroyed the Z3 in 1943, but the incomplete Z4 survives the war's end in a basement.
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.)
The ENIAC's architecture resembles that of the Harvard Mark I, but its components are entirely electronic, incorporating 17,468 vacuum tubes. The machine weighs 30 tons, covers about 1000 square feet of floor, and consumes 130 or 140 kilowatts of electricity.
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, and also incorporates circuits to add a number from a bus 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, with which Mauchly was acquainted.
(The BRL wanted the ENIAC to use on the difficult problem of making aiming tables for use by artillerymen. It isn't ready in time for the war, and overruns its original budget by 225% -- problems that will face Eckert and Mauchly again on later projects.)
Aiken predicts that the United States will need a total of six electronic digital computers.
(As noted below, some early machines will use drums as main memory rather than secondary memory.)
(The term "bug" was of course already in use; that's why it's funny.)
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.
It uses a new type of memory developed by F. C. Williams (possibly after an original suggestion by Presper Eckert), which 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.) This 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 then existing. The Mark I's main memory of 32 32-bit words occupies a single Williams tube. (Other CRTs on the machine are less densely used: one contains only an accumulator.)
The Mark I's programs are initially entered in binary on a keyboard, and the output is read in binary from another CRT. Later Turing joins the team (see also the "Pilot ACE", below) and devises a primi- tive form of assembly language, one of several developed at about the same time in different places.
(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.)
All machines first mentioned in the chronology from here on are stored-program computers.
The Whirlwind is the first computer designed for real-time work; it can do 500,000 additions or 50,000 multiplications per second.
(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...)
This is the first full-scale operational stored-program computer, and is therefore the final candidate for the title of "the first computer".
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 Presper Eckert had made an improved version in connection with radar systems. It works by repeatedly converting from the usual electrical data pulses to ultrasonic pulses directed along, typical- ly, 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 1500 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.
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.
(A successor to this machine will be named "DEUCE".)
Zuse's Z4 is finally completed and goes into service at ETH (Federal Polytechical 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.
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.
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.
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 2048 or 4096 36-bit words of CRT memory; it does 2200 multipli- cations 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.)
Grace Murray Hopper implements the first compiler, the "A-0". (But as with "first computer", this is a somewhat arbitrary designation.)
"The age of chivalry is gone. That of sophisters, economists, and calculators, has succeeded; and the glory of Europe is extinguished for ever." -- Burke, 1792
This article is in the public domain.