Darren New <dne### [at] sanrrcom> wrote:
> Warp wrote:
> >   2's complement binary registers require simpler circuitry to be operated
> > with, compared to BCD registers, hence making the CPU design simpler (and
> > hence less expensive).
>
> Until it's time to scale the decimal place.
>
> Add a 30-digit number with two decimal places to a 30-digit number with 4
> decimal places in binary.
>
> Now do the same in BCD.
>
> But, surely, Intel's mainframe CPU division doesn't know anything about
> efficiency of instructions and data.
>
> --
> Darren New, San Diego CA, USA (PST)
>     C# - a language whose greatest drawback
>     is that its best implementation comes
>     from a company that doesn't hate Microsoft.

Another reason for retaining hardware decimal instructions would be for backward
compatibility.  The company I work for has thousands of cobol programs that use
decimal instructions. It would be impossible to upgrade to the new processor
without that feature.  IBM has to insure the upgrade path for it's customers is
as painless as possible.

Isaac.

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