# ABC - Computer An Atanasoff - Berry - Computer Simulation

With a simulation program for the PC
as of Dec 9, 2019

Recent changes

 The Web This web site

Table of Contents
 Link to video The ABC in Operation A great introduction - BACKGROUND Documentation Needed Simulation Goal Graphical User Interface Pages from the Burks & Burks book Notes ABC - Proof Of Concept Device Uses for the ABC machine? ABC - may have had a User, Dr. Snedecor From the school of hard knocks Examples Debugging ... ABC by Charles Shorb Presentation by John V. Atanasoff about the ABC- at Computer Museum (in Boston) another description and simulation of ABC, added Sept 2014 The Quest for Linear Equation Solvers and the Invention of Electronic Digital Computing, added Oct 2014 original .doc Detailed Pictures of reconstruction at CHM

From the school of hard knocks
 The algorithm on page 269 (above) has been simplified too much - There needs to be a check for the pivot CA being zero after the arithmetic, if zero, stop, go to next pivot. Many simple examples of integer simultaneous equations with known integer solutions give wildly incorrect results with Atanosoff's ratioing - unless scaled up by factors of say 10000. This link provides examples with exact and non-exact answers as run under Atanosoff rules. A further problem, somewhat alleviated by more scaling, is where the coefficients differ by several orders of magnitude. a small coefficient not on the pivot can get shifted right to become zero very early in the ratioing cycle - introducing further inaccuracies. It is easy to imagine that Atanosoff selected the large fixed point capability - 50 binary bits or about 15 decimal places to help fight the above problems. You may begin to appreciate floating point computations which (usually) eliminate the scaling problems noted above. We are so spoiled, and can work so much faster, and confidently, with much less concern about various overflows and underflows. I am so thankful -

If you have comments or suggestions, Send e-mail to Ed Thelen