From: quadibloc@ca.invalid   
      
   On Wed, 11 Feb 2026 17:57:29 -0600, David Schultz wrote:   
   > On 2/11/26 5:04 PM, quadi wrote:   
      
   >> I remember having read one article in a computer magazine where someone   
   >> mentioned that an unfortunate result of the transition from the IBM   
   >> 7090 to the IBM System/360 was that a lot of FORTRAN programs that were   
   >> able to use ordinary real nubers had to be switched over to double   
   >> precision to yield acceptable results.   
      
   > This reminds me of when I took a numerical analysis course. (The many   
   > ways that computer calculations can go wrong and how to deal with it.)   
   > The professor said that the schools IBM (360 or 370, ca. 1980) was   
   > perfect for the course because of the defects in its floating point   
   > system. Guard digits and rounding sorts of things as near as I can   
   > recall.   
      
   Mitch Alsup mentioned that there was no guard digit in the floating-point   
   arithmetic units of the various IBM System/360 models when they were   
   initially released. However, this was so serious an omission, as was   
   quickly noted in practice, that IBM quickly modified the design, and   
   refitted all the units in the field.   
      
   Even after this was done, though, since the exponent in IBM floating-point   
   was a power of 16 rather than 2, and since floating-point calculations   
   were truncated rather than rounded on the System/360, its floating-point   
   was still considered to be less than the greatest.   
      
   There were workarounds, though, which people have mostly forgotten about   
   due to the ubiquity of IEEE 754 floating-point these days. A famous   
   numerical analysis textbook which explained how to cope with the problems   
   caused by substandard floating point formats was _Floating-Point   
   Computation_ by Pat H. Sterbenz.   
      
   John Savard   
      
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