[e2e] OT: a different number base

[Stephen Casner]

On Wed, 2 Apr 2003, Stephen Wolff wrote:

> The IBM 650 was a base-10 machine, but the notation/representation was
> biquinary - i.e., "which hand? which finger?" as it were...
> see for example <http://www.msoe.edu/~kocourek/Codes.PDF>  -s

The IBM 1620 (1960's era) was another base-10 machine using 6-bit
memory cells to store binary-coded decimal plus a flag bit and a
parity bit.  Three of the 6 extra codes were also used for special
markers.  The flag bit was used to mark the end of a string of memory
cells composing a number, so the precision of the arithmetic was
arbitrary up to memory size (which was a maximum of 60,000 digits).
Floating point numbers could have up to 100 digits of mantissa.

Furthermore, on the Model I, both addition and multiplication were
performed using tables stored in memory.  For fun, the tables could be
reloaded to change the number base to something less than 10.  Because
the "9's complementer" was implemented in hardware, though, addition
of negative values or subtraction would only work for bases up to 4.

More info at:  http://www.wikipedia.org/wiki/IBM_1620

One of these computers has been restored to operation at the Computer
History Museum in Silicon Valley:

http://www.computerhistory.org/old/IBM1620/

                                                        -- Steve