TheORDVAC (OrdnanceDiscreteVariableAutomaticComputer), is an earlycomputer built by theUniversity of Illinois for theBallistic Research Laboratory atAberdeen Proving Ground.[1] It was a successor to theENIAC (along withEDVAC built earlier). It was based on theIAS architecture developed byJohn von Neumann, which came to be known as thevon Neumann architecture. The ORDVAC was the first computer to have acompiler[citation needed]. ORDVAC passed its acceptance tests on March 6, 1952, at Aberdeen Proving Ground in Maryland.[2][3]: IV [4] Its purpose was to perform ballistic trajectory calculations for the US Military. In 1992, theBallistic Research Laboratory became a part of theU.S. Army Research Laboratory.
Unlike the other computers of its era, the ORDVAC andILLIAC I were twins and could exchange programs with each other. The laterSILLIAC computer was a copy of the ORDVAC/ILLIAC series. J. P. Nash of the University of Illinois was a developer of both the ORDVAC and of the university's own identical copy, theILLIAC, which was later renamed the ILLIAC I. Abe Taub, Sylvian Ray, andDonald B. Gillies[5] assisted in the checkout of ORDVAC at Aberdeen Proving Ground. After ORDVAC was moved to Aberdeen, it was used remotely by telephone by the University of Illinois for up to eight hours per night. It was one of the first computers to be used remotely and probably the first to routinely be used remotely.
The ORDVAC used 2178vacuum tubes. Its addition time was 72microseconds and the multiplication time was 732 microseconds. Itsmain memory consisted of 1024words of 40bits each, stored usingWilliams tubes. It was a rareasynchronous machine, meaning that there was no central clock regulating the timing of the instructions. One instruction started executing when the previous one finished.
Among the ORDVAC programmers wereMartin Davis[6] andElsie Shutt.
ORDVAC and its successor at Aberdeen Proving Ground,BRLESC, used their own unique notation forhexadecimal numbers. Instead of the sequence A B C D E F universally used today, the digits ten to fifteen were represented by the letters K S N J F L (King Sized Numbers Just For Laughs), corresponding to theteleprinter characters on five-trackpaper tape. The manual that was used by the military in 1958 used the name sexadecimal for the base 16 number system.
When ORDVAC was completed, it was tested at the University of Illinois and then disassembled and shipped toAberdeen Proving Ground inMaryland. Three faculty members including Sylvian Ray and Abe Taub drove to Maryland to help assemble the machine, which was reconstructed and passed its validation tests in just a week. It was expected that assembly and testing would take over a month. When some military officers came to check on the progress of Ordvac assembly, they asked, "Who is in charge here?", and were told, "It's the guy who is holding the broom!", as Abe Taub—the head of The University of Illinois Digital Computer Laboratory—was sweeping up after having completed all the necessary tasks.[7]
Total of 2718 vacuum tubes,[3]: 4 weight 3,000 pounds (1.5 short tons; 1.4 t).[8]
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