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From: jack@mcvax.uucp (Jack Jansen)
Newsgroups: comp.unix.wizards
Subject: Re: CYBER word length
Message-ID: <7147@boring.mcvax.UUCP>
Date: Sat, 15-Nov-86 10:14:17 EST
Article-I.D.: boring.7147
Posted: Sat Nov 15 10:14:17 1986
Date-Received: Sun, 16-Nov-86 01:35:30 EST
References: <7208@elsie.UUCP> <5142@brl-smoke.ARPA> <2447@hcr.UUCP> <363@yabbie.rmit.oz> <612@astroatc.UUCP> <852@zeus.UUCP>
Reply-To: jack@boring.uucp (Jack Jansen)
Organization: AMOEBA project, CWI, Amsterdam
Lines: 31
Apparently-To: rnews@mcvax


In article <852@zeus.UUCP> bobr@zeus.UUCP (Robert Reed) writes:
>In article <612@astroatc.UUCP> philm@astroatc.UUCP (Phil Mason) writes:
>>The Cyber word length was selected to be 60 bits because of the number of 
>>exact divisors it has : 2, 3, 4, 5, 6, 10, 12, 15, 20, and 30.
>
>That's a great myth.  Almost believable.  But isn't it true that the Cyber
>word length was set a 60 bits to be compatible with the old CDC-6000 series?
>Isn't the operant concern here to be a multiple of 6?
Well, a Cyber isn't really the successor of the CDC-6000 series, as
far as I know, it's the same thing. At some point, they changed the
name CDC-6000 series into CDC Cyber 60 (and then 70, etc.).

60 bits was very convenient, since it was not only 10 6-bit charachters,
but also 4 15-bit instructions.

A long time ago, someone told me the following story to explain
the 60 bit wordlength. Note that I don't really believe it, it's
probably too good to be true.

At some time, the DoD (or some equally powerful body) said they would,
from now on, only buy 64 bit machines, which supported an 8 bit
character set.
Control Data, being fairly sure of the fact that their machine would
be bought *anyway*, because the immense performance gap between it and
it's nearest competitors, decided not only to build a machine with
6 bit characters, but also use 60 bit words, so that it would be
virtually impossible to transfer tapes containing any binary data
from their machine to anything else......
-- 
	Jack Jansen, jack@mcvax.UUCP
	The shell is my oyster.