Diff between 11/20 and 11/45?

Dave Horsfall dave at fgh.geac.com.au
Tue Sep 7 14:13:30 AEST 1999

On Tue, 7 Sep 1999, Warren Toomey wrote:

> I've got a few working. cat works. ls and date run, but sort of give
> strange outputs.

What sort of strange output?  My guess is that kernel-wise, date-handling
would have changed.

> These executables were written for a PDP-11/20. Are there any significant
> USER-MODE differences between the 11/20 and later PDP-11 models? I'm
> thinking missing instructions, different addressing mode behaviour etc.

Ummm...  No floating point (all emulated), and I seem to recall that
it didn't even have multiply/divide; could this be the problem?  The
/20 was certainly a subset of the "classic" 11.  No memory management,
but users won't see that.  Also had some quirks, long-forgotten.

My experience is based on the GT-40, which was basically a /20 with a
graphics processor attached to it (which had a mean Lunar Lander game!).

Dave Horsfall VK2KFU  dave at geac.com.au  Ph: +61 2 9978-7493 Fx: +61 2 9978-7422
Geac Computers P/L (FGH Division) 2/57 Christie St, St Leonards 2065, Australia

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