PDP-11/83 w/FPU?

Josh Dersch derschjo at gmail.com
Wed Apr 17 23:44:20 CDT 2019

On Wed, Apr 17, 2019 at 2:58 PM Paul Koning via cctalk <
cctalk at classiccmp.org> wrote:

> > On Apr 17, 2019, at 4:36 PM, Ethan Dicks via cctalk <
> cctalk at classiccmp.org> wrote:
> >
> > On Wed, Apr 17, 2019 at 2:48 PM W2HX via cctalk <cctalk at classiccmp.org>
> wrote:
> >> ?Hi friends. I am putting together a PDP-11 set up. i have a few CPUs
> available to me, a 11/23+, an 11/73 and I also have available to me an
> 11/83, M8190-AE .
> >>
> >> I would like to try to run as many different OS's as may interest me,
> including some unixes as possible (bsd...etc).  My question is, are there
> any OSes that need the floating point option?
> >
> > I know old UNIX (v2) needs a KE11-A or KE11-B (a Unibus peripheral
> > integer math option), which really wasn't something people
> > bought/installed in an 11/34 or later.  v5, v6, and v7 UNIX shouldn't
> > require any sort of math hardware.
> I think that was typically called "EAE" (extended arithmetic element), a
> Unibus peripheral that implemented integer mul/div and maybe a few other
> odds and ends.  RSTS V4 had optional support for that.  It only applies to
> 11/20 and 11/05 since all the other machines have the relevant instructions
> built into the CPU.  (Later versions of RSTS required that.)

The EAE was also an option on the 11/40.

At any rate, on the 11/73 and 83 CPU, the microcode emulates the floating
point instructions if an actual FPA isn't fitted, so everything should just
work (just a bit slower).

- Josh

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