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From: greg@sdcsvax.UUCP
Newsgroups: net.unix-wizards
Subject: Re: IBM 1620 10000x10000 digit multiplication
Message-ID: <760@sdcsvax.UUCP>
Date: Mon, 7-May-84 00:46:54 EDT
Article-I.D.: sdcsvax.760
Posted: Mon May  7 00:46:54 1984
Date-Received: Tue, 8-May-84 03:31:31 EDT
References: <1347@brl-vgr.ARPA>
Organization: EECS Dept. U.C. San Diego
Lines: 21

Another dinosaur speaking.....  Multiplication and division on the 1620
were complicated by the fact that it utilized a scratchpad area in low
memory (memory locations 99, 98, 97, ...) but only twenty characters of
it (80-99) were cleared to zero before executing the operation.  If you
had a multiply/divide that would use more than this scratchpad, you had
to clear it yourself.  Also, since memory wrapped around from the very
largest location to the smallest (and vice versa) you had to be very
careful where you located your operands so that they wouldn't get clobbered
by the intermediate results being generated in the scratchpad.

I once divided two numbers that were almost 10,000 digits -- as I recall,
they were actually about 9,800 and 9,200 digits.  It took a LOT longer than
a few seconds.  I didn't time it, but my memory was that it took at least
ten minutes.  It was long enough for me to phone the prof for whom I was
doing the work, tell him that his job was in the final divide, and have
him walk over to the computer lab before it finished!

A wonderful machine -- I miss it.

-- 
-- Greg Noel, NCR Torrey Pines       Greg@sdcsvax.UUCP or Greg@nosc.ARPA