Path: utzoo!attcan!uunet!lll-winken!ames!amdahl!nsc!voder!dtg.nsc.com!des
From: des@dtg.nsc.com (Desmond Young)
Newsgroups: comp.arch
Subject: Re: IBM S/360 FP (was Re: RS6000 Multiply/Accumulate instruction)
Summary: Higher Base
Message-ID: <776@blenheim.nsc.com>
Date: 20 Mar 90 19:07:37 GMT
References: <8888@boring.cwi.nl> <8370@hubcap.clemson.edu>
Distribution: comp
Organization: National Semiconductor, Santa Clara
Lines: 30

In article <8370@hubcap.clemson.edu>, mark@hubcap.clemson.edu (Mark Smotherman) writes:
> From article <8888@boring.cwi.nl>, by dik@cwi.nl (Dik T. Winter):
> > complete (although one still wonders why they ever chose for hex arithmetic).
>   The Bendix G20 (1961) pioneered the use of a higher power of 2 as base
> by selecting base 8.  In the design of System/360, ..., we were using a

Actually, I wonder if that is the case. Burroughs have used octal base
since their first stack machines. The B5000(?) was circa 1960, I suspect
their use may predate the Bendix.
  Anyway, a higher radix does lose some precision, i.e. when
normalized, there may (or may not) be a loss of significant digits.
There was a paper
  (pause while he digs through old boxes)...
  Yes:
      "On the Precision Attainable with Various
	Floating-Point Number Systems"
      by Richard P. Brent
      IEEE Transactions on Computers, Vol C-22 Number 6.

  My reading was, binary with an implicit leading bit is of course
the best, and up to base 4 was ok. However, there does seem to be
benefit for choosing even 8 over 16.

  On another tack, Burroughs have traditionally also made decimal
machines. The financial community loved it. I think they had
24 decimal-digit precision. I do not need to add any more to a
previous posting about all those fractions of a cent adding up..

Des.
   des@dtg.nsc.com