Invalid system disk?

Although the IBM 1620's architecture was very popular in the scientific and engineering community, computer scientist Edsger Dijkstra pointed out several flaws in its design in EWD37, "A review of the IBM 1620 data processing system" (see http://www.cs.utexas.edu/users/EWD/index00xx.html at the Dijkstra archive at the University of Texas).