Path: utzoo!attcan!uunet!decwrl!wuarchive!zaphod.mps.ohio-state.edu!mips!twg.com!dwh
From: dwh@twg.com (Dave W. Hamaker)
Newsgroups: comp.arch
Subject: Re: 1620 (Was Odd word size?  Word size?  Word?  Definitely Odd.)
Message-ID: <8047@gollum.twg.com>
Date: 8 Oct 90 23:30:25 GMT
References: <270CB430.21156@ics.uci.edu> <GOTTLIEB.90Oct5150853@allan.ultra.nyu.edu>
Organization: The Wollongong Group, Palo Alto, CA
Lines: 25

gottlieb@allan.ultra.nyu.edu (Allan Gottlieb) writes:

>In article <270CB430.21156@ics.uci.edu> baxter@zola.ics.uci.edu (Ira Baxter) writes:

>   Earlier 1620s had a multiply instruction which worked by looking
>   up multipler/multiplicand digit pairs in the multiplication table
>   in lower memory.   This table had to be loaded correctly before
>   you used multiply.  There are apocryphal stories of folk loading
>   the table in such a way that multiplies worked in octal rather
>   than the standard decimal.

>I programmed one at Grumman Aircraft in the 60s and believe that it
>was the add tables that were stored.  You had a 10 by 10 array that
>gave the sum (using the mark as carry).  I/O devices were (as
>stated) card reader/punch and typewritter.  Huge I/O edge over paper
>tape in Bendix G15.

The IBM 1620 Model I used both an addition table and a multiplication table
in low memory.  The 1620 Model II did addition in hardware (and probably
multiplication as well, but I'm not certain of that).  The Model I's add
and multiply tables could indeed be configured to operate in octal (in fact,
the tables could be configured operate in bases 2-9).

-Dave Hamaker
dwh@twg.com