Editing IBM 1620 (section)

===Architectural difficulties===
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".<ref>[https://www.cs.utexas.edu/users/EWD/transcriptions/EWD00xx/EWD37.html E.W. Dijkstra Archive: A review of the IBM 1620 Data Processing System (EWD 37)]</ref> Among these are that the machine's Branch and Transmit instruction together with Branch Back allow only one level of nested subroutine call, forcing the programmer of any code with more than one level to decide where the use of this "feature" would be most effective. <!-- The branch-back address could NOT be saved or restored as there was no instruction to do that. --> He also showed how the machine's paper tape reading support could not properly read tapes containing record marks, since record marks are used to terminate the characters read in storage. One effect of this is that the 1620 cannot duplicate a tape with record marks in a straightforward way: when the record mark is encountered, the punch instruction punches an EOL character instead and terminates. However this was not a crippling problem:

* the data can be copied to the end of memory and punched verbatim with a DN instruction instead of WN
* tapes were usually duplicated [[offline]].

Most 1620 installations used the more convenient punched card input/output,<ref>{{cite web|url=http://www.textfiles.com/bitsavers/pdf/ibm/1620/Basic_Programming_Concepts_and_the_IBM_1620_Computer_1962.pdf |archive-url=https://web.archive.org/web/20150720184343/http://www.textfiles.com/bitsavers/pdf/ibm/1620/Basic_Programming_Concepts_and_the_IBM_1620_Computer_1962.pdf |title=Basic Programming Concepts and The IBM 1620 Computer |archive-date=2015-07-20 |quote=The punched card is the most widely used media for communication with machines}}</ref> rather than paper tape.

The successor to the 1620, the [[IBM 1130]],<ref>"Similar demands for small to medium scientific computers resulted in the IBM 1620
and its successor the IBM 1130." {{cite book
|url=https://books.google.com/books?isbn=1483268594   |isbn=978-1483268590 
|title=Computer Organization and Assembly Language Programming
|author1=James L. Peterson  |author2=Werner Rheinboldt   |date=2014}}</ref> was based on a totally different, 16-bit binary architecture. (The 1130 line retained one 1620 peripheral, the [[IBM 1627]] drum plotter.)