from RISKS -- The first programming errors

[David Farber <farber () central cis upenn edu>]

Date: Tue, 7 Sep 93 21:48:36 -0700
From: Jon Jacky <jon () violin1 radonc washington edu>
Subject: The first programming errors


There is an interesting story in THE SCIENCES, July/August 1993: "The
Discovery of Debugging," by Brian Hayes, pps. 10 -- 13.  


It describes experiences programming EDSAC, which the story says was the the
first true stored program computer, at Cambridge in 1949.


EDSAC's first three programs -- which calculated lists of squares and prime
numbers -- worked correctly the first time they were run!  This was no mean
accomplishment, in view of EDSAC's instruction set and the very rudimentary
programming tools available.


After that, it got difficult.  While cleaning his office in 1979, EDSAC
designer Maurice Wilkes came upon a thirty year old punched tape which
contained an early version of a program for calculating a table of values for
Airy's integral.  Wilkes gave a copy to Martin Campbell-Kelly, who studied it
using an EDSAC simulator.


The 126 line program contained 20 errors! Most were trivial typos or logical
errors, but one quite subtle error merely reduced precision in the fifth
decimal place.


The story quotes from a memoir by Wilkes, who recalls the exact moment when
"the realization came over me with full force that a good part of the
remainder of my life was going to be spent finding errors in my own programs."


The SCIENCES story cites an article by Martin Campbell-Kelly in ANNALS OF
THE HISTORY OF COMPUTING 14(4) 1992 and Maurice Wilkes' book MEMOIRS
OF A COMPUTER PIONEER.


- Jon Jacky, Department of Radiation Oncology, U. of Washington, Seattle