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Historical Monograph: Electronic Computers Within the Ordnance Corps.
Source: U.S. Army Photo, from K. Kempf

ORDVAC (Ordnance Variable Automatic Computer) belongs to the group of computers whose basic logic was developed by the Institute for Advanced Study at Princeton, NJ and utilized in a prototype computer developed at the Institute. This ORDVAC family of computers includes such machines as the ILLIAC, ORACLE, AVIDAC, MANIAC, JOHNNIAC, MISTIC, and CYCLONE.

(ILLIAC - Illinois Automatic Computer; ORACLE - Oak Ridge Automatic Computer and Logical Engine; AVIDAC - Argonne Version of the Institute's Digital Automatic Computer; MANIAC - Mathematical Analyzer Numerical Integrator and Computer; JOHNNIAC - John (v. Neumann) Integrator and Automatic Computer; MISTIC - Michigan State Digital Computer; CYCLONE - (an arbitrary name indicating high speed) Iowa State U.) ORDVAC was constructed by the University of Illinois for the Ballistic Research Laboratory at Aberdeen Proving Ground, under a contract from the Ordnance Department. The contract number was, W11-022-ORD-11362--RAD ORDTB 9-10675--ORD PROJ TB3-0007J--negotiated under ASPR 3-205. The contracting agency was the Chicago Ordnance District and the period of the contract was 15 April 1949 to 31 October 1951. ORDVAC became operational in the Spring of 1951 at Aberdeen Proving Ground in Maryland.

Through arrangements made by Dean L. N. Ridenour, the University of Illinois began construction of ORDVAC about 15 April 1949. The efforts of many individuals went into the construction of the machine. The University of Illinois received the cooperation of members of the staff of the Ballistic Research Laboratory in the procurement of materials and the assignment of members of the staff of BRL during the final phases of construction. These BRL staff members were: Dr. P. M. Kintner, Mr. G. H. Leichner, and Mr. C. R. Williams. In addition, Dr. L. A. Delsasso and Dr. R. F. Clippinger followed the work from its inception.

The logical structure of ORDVAC was patterned after a machine described in the 28 June 1946 report, "Preliminary Consideration of the Logical Design of an Electronic Computing Instrument" by Burks, Goldstine and von Neumann of the Institute for Advanced Study. The University of Illinois received helpful information and suggestions arising from discussions with Mr. J. H. Bigelow, Captain H. H. Goldstine and Mr. J. H. Pomerene of the Institute for Advanced Study, especially during the early period of construction of the ORDVAC. Also, drawings pertaining to the arithmetic unit and memory of the machine at the Institute for Advanced Study were furnished to the University of Illinois and some parts of these drawings, such as the registers, were copied for the ORDVAC.


It was first planned to build ORDVAC from circuit drawings obtained from the Institute for Advanced Study, but this intention was later changed and most of ORDVAC was constructed from circuits designed at the University of Illinois. The fundamental flipflop, gating and cathode follower circuits, as employed at the Institute for Advanced Study, were used however. The registers, complement gate and clear drivers were copied from the machine developed at the Institute for Advanced Study and the teletype units were of the kind developed at the National Bureau of Standards for the Institute for Advanced Study. Except for these, however, responsibility for the design of ORDVAC rested with the University of Illinois.

ORDVAC was provisionally accepted by the Ballistic Research Laboratory on the basis of tests conducted between 15-25 November 1951 at the University of Illinois. The machine was dismantled beginning 11 February 1952 and shipped to the BRL on 16 February 1952. During 5-6 March 1952 it successfully performed the three final acceptance tests. These were: (a) the operation of the "final test" routine for twenty hours with one error; (b) the operation of a memory "read-around" test routine requiring that the memory could be consulted ten times at each of its addresses without causing a failure at any other address (this was repeated five times); and (c) the operation of a memory flaw test for thirty minutes without an indication of a failure.

The machine was moved to the Ballistic Research Laboratory under contract: DA-11-022-ORD-680; SUB-RAD 52-56; ORDTB 2-1002; project TB3-0007. The cost of the basic system was approximately $600,000.

The work at the University of Illinois was administered chiefly by an executive committee of the Computer Sub-committee of the University Research Board. This committee consisted of Professor N. M. Newmark, Professor A. H. Taub, Professor R. E. Meagher and Professor J. P. Nash.

The machine was designed to solve the following types of problems:

  1. Exterior ballistics problems such as high altitudes, solar and lunar trajectories, computation for the preparation of firing tables and guidance control data for Ordnance weapons, including free flight and guided missiles.
  2. Interior ballistic problems, including projectile, propellant and launcher behavior, e.g., physical characteristics of solid propellants, equilibrium composition and thermodynamic properties of rocket propellants, computation of detonation waves for reflected shock waves, vibration of gun barrels and the flow of fluids in porous media.
  3. Terminal ballistic problems, including nuclear, fragmentation and penetration effects in such areas as explosion kinetics, shaped charge behavior, ignition, and heat transfer.
  4. Ballistic measurement problems such as photogrammetric, ionospheric, and damping of satellite spin calculations, reduction of satellite doppler tracking data, and computation of satellite orbital elements.
  5. Weapons systems evaluation problems, such as antiaircraft and antimissile evaluation, war game problems, linear programming for solution of Army logistical problems, probabilities of mine detonations, and lethal area and kill probabilities of mine detonations, and lethal area and kill probability studies of missiles.

ORDVAC was a general purpose computer capable of carrying out individual arithmetic operations at high speed. It operated in the binary number system in a parallel asynchronous manner, and originally used an electrostatic memory. Data was originally put into the machine by punched teletype tape, later by punched cards. Data was obtained from the machine on punched cards, a teletype page printer, or punched teletype tape.

The part of ORDVAC capable of carrying out arithmetic operations on numbers supplied to it was called the arithmetic unit. It consisted of three registers (two of them double registers), which were essentially storage units for holding the operands involved in arithmetic operations, a parallel 40- binary digit adder, and other subsidiary units such as the complement gate which provided the complement of the number was one of the registers.

The registers of the arithmetic unit corresponded to the keyboard and dials on the common desk calculator. They held the operands while the operations of arithmetic took place, and they presented the results of these operations. The basic components of the registers were the flipflop and the gate.

ORDVAC was a parallel machine, that is, operations were performed simultaneously on all the digits of an instruction or information word. For example, when a 40-digit number was transferred from the memory into a register of the arithmetic unit, all digits were transferred simultaneously. Similarly, when a number in R3 (one of the registers) was added to a number in the accumulator, the steps in this process were carried out on all the digits at the same time.

Although ORDVAC could use several number systems, the basic one was the binary or base-two system. This system was convenient because it requires only the two digits 0 and 1 for number representation and therefore flipflops or any other two-state devices could be efficiently used. Moreover, the logical structure of the machine was based upon a two-state logic (where all decisions are of the yes-no type), so that an over-all consistency was obtained.

Source:U.S. Army



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