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Manufacturer University of Pennsylvania
Identification,ID -
Date of first manufacture-
Number produced -
Estimated price or cost-
location in museum -

Contents of this page:



  • 20 individual 10 digit accumulators.
  • Accumulators can transmit numbers to other accumulators through the digit output terminals labeled A (for add) and S (for subtract).
  • Similarly, accumulators can receive numbers through 5 digit input terminals, labled Alpha, Beta, ...
  • Timing for transmission and reception of numbers is controlled by pulses received by the program pulse terminals. Each accumulator has twelve program controls. On each accumulator, Program Controls 1--4 are non-repeat controls that perform only one function when they receive a pulse on their program input terminal.

    Program Controls 5--12 are repeat program controls that can perform the same function up to nine times. A repeat program control begins to perform when it receives a pulse on its input terminal. When it is finished, it transmits a pulse on its output terminal

  • 10's Complement Negative numbers are stored in the Eniac by their 10's complement which is computed by subtracting a given number from M 9 999 999 999 and then adding one. For example, to find the way -84 is represented, we perform the subtraction:
        M  9  999  999  999
    -   P  0  000  000  084
        M1 9  999  999  915
    We then add one, to get our result -84 = M 9 999 999 916
  • 1 multiply unit
  • 1 divide unit
  • 1 square root unit
  • 3 function generators
  • All of the above units could be wired (programed) to function in parallel

Special features
  • The most important technical achievement of the Eniac was its lightning speed. The Eniac takes only 200 microseconds to add or subtract. That means that it can perform 5000 addition cycles each second.
  • Another significant feature of the Eniac is its ability to perform digit discrimination and branch loops. The Eniac was the first machine to support common ``if statements'' that are so vital to the execution of useful programs.
  • Despite all its similarities to today's computers, the Eniac maintains some important differences. The main one is that it can not store its programs electronically. Programs must be hard-wired before the machine is started. The other interesting difference is that the machine is ``synchronous.'' The timing of all instructions is set up before a program is begun.
  • A Short History of the Second American Revolution states that the mean time between failures was greater than 12 hours, This was gained by"
    • Lower power levels and careful design alternatives were sought to minimize the amount of work demanded of the vacuum tubes.
    • Most tubes were found to fail early or late in their lives, which resulted in a regimen of preventive maintenance ensuring that only the healthiest" tubes were used in the ENIAC.
    • Eckert instituted rigid requirements for careful design and construction that had to be met by all engineers and technicians on the project where even a faulty soldering joint could render the entire machine useless.
    • Universal design standards, established collaboratively by all of the Moore School engineers ensured that components such as resistors, as well as the vacuum tubes, operated at a certain percentage of their rated capacity. "
  • from alt.folklore.computers "According to the official specs, the ENIAC used 17,468 tubes, but only 16 different types of tubes. (as reproduced in Nancy Stern's "From ENIAC to UNIVAC" for whatever it is worth)."

Historical Notes
At some later date, ENIAC was converted to a stored program machine.

This Specimen
- This unit is one of the twenty accumulators. there were also other types of units such as a multiplier, 3 function generators, and switch input panels. The whole unit filled a very large room, and had 18,000 vacuum tubes.

Interesting Web Sites

  • The ENIAC Story by Martin H. Weik, 1961

  • working prototype of an ENIAC simulator with up to 20 accumulators, initiating, and cycling unit. It is Java Applet and you can wire your own programs. There are still some bugs, but the thing works! (E-mail from Raul in Berlin to Dag Spicer - May 13, 2004)

  • A Tribute to Dr. J. Presper Eckert Co-Inventor of ENIAC - courtesy Dan McGrath

  • Dr. Mike Williams has The Electronic Numerical Integrator and Computer (ENIAC) by H.H. Goldstine and Adelle Goldstine in his web site.

  • [Link now dead :-( ] Simulation of the ENIAC, A very comprehensive study of the machine. Gives an appreciation why no one would never architect or design a machine that way again.

  • Electronic Computers within the Ordnance Corps - Chapter II -- ENIAC

  • ENIAC History - has some on line documents

  • ENIAC-on-a-Chip, Moore School of Electrical Engineering, "The original ENIAC was programmed by physically connecting one module to another with cables. For "ENIAC-on-a-Chip", this has been accomplished by pre-connecting every possible input and output of every module and mediating the conduction of the connections with programmable switches. These switches can be programmed by an external source, e.g. a PC, which will determine the "cables" that conduct, thus achieving the desired effect."

    and from alt.folklore.computers
    My nomination for Useless Hack of the Computer Era:

    A professor at U P had his students cook up designs for ENIAC on a CHIP, a project that was quite successful.

    Even before the production run, I asked to buy one, figured it would be a kick to have something that could be stuck on a PCI board and (since the chip had the ability to connect any ENIAC unit connectable to any other in the original) to program the entire Moore School machine room in Visual Basic, displaying and allowing the plugging and setting of every ENIAC module for a run, maybe even adding in a random 3 hour MTBF tube killer.

    After much e-mail, I was informed that since so few chips were made, they were only available to museums and academic institutions. "Find a fab, run 'em off and sell 'em" I replied, to no avail.

    It would be tempting, since there was some NSF money involved, to gain the masks through a Freedom of Information Act request, something I'll be glad to help anyone willing to volunteer a fab with. - dmr

Other information
  • If you feel threatened by assembly language programming, you would go crazy "programming" an ENIAC.
  • Two of the 6 original ENIAC programmers spoke at the 2000 ACM Awards Banquet
  • Kathy Kleinman of the ACM (legal staff?) is writing a book, and has a large number of high quality photographs
  • pieces of ENIAC at ?
    • Arthur Burkes - computer science? - has 4 accumulators
    • Univ of Penn
    • Smithsonian - has enough to do a demo
    • West Point
    • University of Michigan (Ann Arbor) EECS building
    • The Eckert estate was auctioned off by Skinner of Boston. There was apparently a piece(s) of the Eniac. News group alt.folklore.computers had "Philadelphia Inquirer for Friday, April 28, 2000, page E8, reports that the lot was sold at the Skinner auction for $79,500, but does not state who was the buyer."
  • Sounces
    • "ENIAC" by Scott McCartney, (reviewers say very non-technical, newspaper like)

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Updated May 14, 2012