Computer History
Tracing the History of the Computer

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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