ORDVAC

From Wikipedia, the free encyclopedia

The ORDVAC or Ordnance Discrete Variable Automatic Computer, an early computer built by the University of Illinois for the Ballistics Research Laboratory at Aberdeen Proving Ground, was based on the IAS architecture developed by John von Neumann, which came to be known as the von Neumann architecture. The electrical engineers at The University of Illinois were the first to complete a computer implementation based upon this design, and that first computer was ORDVAC. The ORDVAC was the first computer to have a compiler. ORDVAC became operational in the Spring of 1951 at Aberdeen Proving Ground in Maryland. Its purpose was to perform ballistic trajectory calculations for the US Military.

Unlike the other computers of its era, the ORDVAC and ILLIAC I were twins and could exchange programs with each other. The later SILLIAC 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, the ILLIAC, which was later renamed the ILLIAC I. Donald B. Gillies 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 2178 vacuum tubes. Its addition time was 72 microseconds and the multiplication time was 732 microseconds. Its main memory consisted of 1024 words of 40 bits each, stored using Williams tubes. It was a rare asynchronous machine, meaning that there was no central clock regulating the timing of the instructions. One instruction started executing when the previous one finished.

ORDVAC and its successor at Aberdeen Proving Ground, BRLESC, used their own unique notation for hexadecimal 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, corresponding to the teletype characters on 5-track paper tape.