Diff between 11/20 and 11/45?

Johnny Billquist bqt at Update.UU.SE
Thu Sep 9 19:58:19 AEST 1999

On Tue, 7 Sep 1999, Warren Toomey wrote:

> 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.

As far as I can remember, there aren't any huge differences. However, some
stuff behave differently in the 11/20. On the other hand, some stuff
behave differently in just about every implementation...

Condition flags on some instructions specifically. And the 11/20 might
have had some limitations on using the PC which differed as well.

I have a processor handbook for the "modern" -11s, which has a chart with
all differences between different models. I started writing it down, to
place in the PDP-11 FAQ, but haven't come that far yet...


Johnny Billquist                  || "I'm on a bus
                                  ||  on a psychedelic trip
email: bqt at update.uu.se           ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol

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