[ih] bytes [Re: "network unix"]

[Brian E Carpenter]

I forget the details, but there was actually a hardware bug in one instruction
in the first PDP-11 model. The decrement of R7 was performed at the wrong point
in the cycle compared with what the ISP definition said, or something like that.
Since R7 was used as the stack pointer, this mattered if you stacked and unstacked
the value of R7. I recall that the original version of FOCAL for the PDP-11 crashed
horribly on later models, because it used some tricky code involving stacking the
stack pointer.

Regards
   Brian

On 12/10/2016 03:18, John Day wrote:
> The thing I remember about this (not much) ;-) is that they didn't understand that auto-increment, auto-decrement addressing modes should be on opposite sides of the instruction so they can be used for stack operations.  I figured it was an indicator.
> 
> 
>> On Oct 11, 2016, at 09:44, Scott Bradner <sob at sobco.com> wrote:
>>
>> this is the story I remember at the time -almost all of  the DG founders were all ex-DEC people
>> particularly Ed de Castro who ran the PDP-8 stuff for DEC - the Nova was basically a glorified PDP-8
>>
>> Scott
>>
>>> On Oct 10, 2016, at 3:32 PM, Noel Chiappa <jnc at mercury.lcs.mit.edu> wrote:
>>>
>>>> From: "John Levine" <johnl at iecc.com>
>>>
>>>> There was a competing 16 bit word addressed design by the designer of
>>>> the PDP-8, which after DEC rejected it became the DG Nova.
>>>
>>
>>
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