The ENIAC may or may not have been the first of its kind—the first fully functional, all-electronic, general-purpose, digital computer—but there’s no doubt it was the last of its kind. They never built another one like it. Computers designed just a few years later seem reasonably familiar in their gross anatomy, but the ENIAC was a creature from another world. A program for the ENIAC was not a sequence of instructions to be executed one after another; it was a configuration of patchcords and plugboards, directing the flow of data from one calculating unit to another.
Ruth Gorden and Ester Gerston wire an ENIAC plugboard circa 1946. U.S. Army photo from http://ftp.arl.mil/ftp/historic-computers/
For the first time in many years it’s now possible to watch the ENIAC in action; if you’re ambitious, you can even try wiring up the plugboard for a problem of your own choosing. Till Zoppke and Raúl Rojas of the Freie Universität Berlin have created an ENIAC simulator in the form of a Java applet, which they describe in the latest IEEE Annals of the History of Computing. (This year is the 60th anniversary of the ENIAC’s public debut, and so the Annals have a series of celebratory articles.)
Unfortunately, I haven’t been able to play with the simulator myself because of a mysterious bug or incompatibility. Deep in the bowels of my Java Virtual Machine there must be a patchcord in the wrong plugboard.