two's complement, was Re: Now OT

Camiel Vanderhoeven iamcamiel at
Thu Jun 23 09:50:35 CDT 2016

On Thu, Jun 23, 2016 at 4:31 PM, Paul Koning <paulkoning at> wrote:
> Another interesting aspect where people may not be aware of how much
> variety existed is in the encoding of floating point numbers.  IEEE
> is now the standard, but PDP-11 users will remember the DEC format
> which is a bit different.  CDC and IBM were different still.  The
> Dutch machine Electrologica X8 had a particularly interesting
> approach (parts of which were adopted, many years later, by the IEEE
> standard).

DEC floating point is still very much around, as VAX floating point.
Alpha had both IEEE and VAX floating point, and compilers on VMS
defaults to VAX floating point. On Itanium CPU's, the chip only has
IEEE floating point, but VAX floating point formats are provided by
the OS, and many customers still compile their code to use VAX
floating point formats.

There are many, many varieties of floating point formats. This page
gives a nice overview:


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