Talk:Pathological floating point problems

mention of the IBM 1620 in the FORTRAN entry

The IBM 1620 (a decimal computer) can support integer arithmetic up to the size of the machine; it came in twenty, forty, or sixty thousand decimal digits (a digit consisted of six bits:

 a check bit     (nowadays, this would be called a parity bit)
 a flag bit      (for negative numbers, indirect addressing, end of field) 
 4 numeric bits  (a decimal digit, or one-half of a character)

The IBM 1620 model I had tables for addition and multiply (stored in low memory), so it shouldn't be overlaid if one expects to perform integer arithmetic. However, modifying these tables enabled arithmetic in other bases (up to base ten).

My first exposure to a computer was during a tour of the computer room (1965), the teacher entered (typed) a machine-language program into the computer memory (via the typewriter), and the computer program raised 999 to the 999^th power, and it typed 2,997 decimal digits.

There were no control cards for any model of the IBM 1620.

The IBM 1620 model II removed the need to store those tables in low memory.

For the (optional) floating point feature, the maximum mantissa size was 99 decimal digits, and the exponent was fixed at two decimal digits.

-- Gerard Schildberger (talk) 18:00, 16 February 2017 (UTC)