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ORDVAC (Ordnance Discrete Variable Automatic Computer)

Overview

The ORDVAC was an early electronic computer built at the University of Illinois under contract from the Ballistic Research Laboratory at Aberdeen Proving Ground, Maryland. Based on the IAS von Neumann architecture, it passed acceptance tests on March 6, 1952, and was used for military ballistic trajectory calculations. It was the twin of ILLIAC I – the first pair of computers in history to share an instruction set and exchange programs. ORDVAC was also one of the first computers to be used remotely and probably the first to be routinely used remotely.

Technical Specifications

Specification Detail
Word length 40 bits
Main memory 1024 words of 40 bits, Williams tube storage (40 cathode ray tubes)
Total vacuum tubes 2178 (some sources cite 2718)
Arithmetic unit tubes ~1100
Control unit tubes ~500
Memory tubes ~800 (for Williams tube circuits)
Addition time 72 microseconds
Multiplication time 732 microseconds
Architecture Asynchronous (no central clock); one instruction started executing when the previous finished
Weight 3000 pounds (1.4 metric tons)
I/O Five-track paper tape using teleprinter
Hexadecimal notation Digits 10–15 represented as K, S, N, J, F, L (mnemonic: “King Sized Numbers Just For Laughs”)

Design and Construction History

Contract and Personnel

The Ballistic Research Laboratory awarded a contract to the University of Illinois to build a computer for military use. The contract cleverly required two of every component, which allowed Illinois to build a second identical machine (ILLIAC I) simultaneously.

Key personnel:

  • Ralph Meagher: Chief engineer
  • Abraham H. (Abe) Taub: Head of the Digital Computer Laboratory at Illinois
  • J. P. Nash: Developer of both ORDVAC and ILLIAC I
  • Donald B. Gillies: Assisted with assembly and checkout
  • Sylvian Ray: Assembly and checkout at Aberdeen
  • Martin Davis: Programmer (later famous for the Davis-Putnam algorithm)
  • Elsie Shutt: Programmer

Construction Timeline

  • 1950–1951: Construction at the University of Illinois
  • Early 1952: Tested at the University of Illinois, then disassembled and shipped to Aberdeen Proving Ground
  • Assembly at Aberdeen: Three faculty members, including Sylvian Ray and Abe Taub, drove to Maryland to reassemble the machine. What was expected to take over a month was completed and passed validation tests in just one week.
  • March 6, 1952: Passed acceptance tests at Aberdeen Proving Ground

Key Innovation: Twin Machines

ORDVAC and ILLIAC I were identical twins – the first computers ever to run the same instruction set and exchange programs. This was remarkable for the era, when every computer was essentially a one-of-a-kind machine incompatible with all others.

What Science Was Done on It

Military Applications

ORDVAC’s primary purpose was performing ballistic trajectory calculations for the U.S. Military at Aberdeen Proving Ground. This was a continuation of the calculating work that had driven the development of ENIAC at the same facility.

Remote Computing Pioneer

After ORDVAC was moved to Aberdeen, the University of Illinois used it remotely by telephone for up to eight hours per night. It was one of the first computers to be used remotely and probably the first to be routinely used this way – a precursor to modern remote computing.

First Compiler

ORDVAC is claimed to have been the first computer to have a compiler, though the details of this claim vary across sources.

Notable Anecdotes

  • One-week assembly: The reassembly at Aberdeen that was expected to take “over one month” was completed and passed all tests in a single week – a testament to the engineering quality and the team’s intimate knowledge of the machine.
  • King Sized Numbers Just For Laughs: The unusual hexadecimal notation (K, S, N, J, F, L for 10–15) was dictated by the available characters on the five-track teleprinter paper tape system.
  • Night shift computing: The remote telephone use, where Illinois scientists worked on the machine for eight hours each night while Aberdeen used it during the day, was an early form of time-zone-based resource sharing.

Decommissioning and Current Status

  • Components of ORDVAC came to the Smithsonian Institution (National Museum of American History) from Aberdeen Proving Ground in 1962.
  • In 1992, the Ballistic Research Laboratory at Aberdeen became part of the U.S. Army Research Laboratory.
  • ORDVAC components are held in the Smithsonian’s collection. Some components are on display at the Siebel Center at the University of Illinois (first floor hallway, ILLIAC Series display).

Sources

  • “ORDVAC,” Wikipedia. https://en.wikipedia.org/wiki/ORDVAC — Accessed: 2026-04-02
  • “ILLIAC and ORDVAC,” Illinois Distributed Museum. https://distributedmuseum.illinois.edu/exhibit/illiac_and_ordvac/ — Accessed: 2026-04-02
  • “Mainframe Computer Component, Digital Resolver Plug in Chassis for ORDVAC Computer,” Smithsonian. https://americanhistory.si.edu/collections/object/nmah_1368477 — Accessed: 2026-04-02
  • “Mainframe Computer Component, Plug-in Unit for the ORDVAC Computer,” Smithsonian. https://americanhistory.si.edu/collections/object/nmah_1368471 — Accessed: 2026-04-02
  • “A review of ORDVAC operating experience,” ACM Digital Library. https://dl.acm.org/doi/10.1145/1434878.1434899 — Accessed: 2026-04-02
  • “HISTORICAL MONOGRAPH” (U.S. Ordnance). https://ed-thelen.org/comp-hist/U-S-Ord-61.html — Accessed: 2026-04-02