[Simh] pdp11 and unix

[Paul Koning]

> On Feb 29, 2016, at 1:21 AM, lists at openmailbox.org wrote:
> 
> On Sat, 27 Feb 2016 17:32:19 -0500
> Paul Koning <paulkoning at comcast.net> wrote:
> 
>> Decimal did show up at times even into the 1960s, for example in the IBM
>> 1620.  But it never made all that much sense; converting between binary
>> and decimal is quite easy even in those very old machines.  The one
>> plausible application area is business data processing where the
>> arithmetic is trivial and most of the work is I/O or other non-arithmetic
>> operations.
> 
> IBM S/360 (1964) and follow-ons have all had hardware support for decimal
> and COBOL and PL/I on these platforms have always had native suport for the
> data type.
> 
> As you might expect decimal arithmetic is used extensively in financial
> transactions and reporting since there is no problem of conversion. Money
> can be represented exactly rather than approximately as with floating
> point. Most banks still run their financial transactions on IBM hardware
> and OS for that reason among others.

Most 360s, actually; the 360 model 44 didn't have decimal instructions (except via an emulator -- like the later microVAXen with their subset instruction sets).

I wasn't referring to packed decimal instructions for binary machines; those stayed around for a long time.  Even VAX had them, at least originally.  I was talking about decimal machines, with memories organized in decimal digits.  The last computer I can think of that fits that description is the IBM 1620, from the early 1960s.

	paul