[TUHS] Harvard and Von Neumann Architectures and Unix

Jon Steinhart jon at fourwinds.com
Sat Nov 25 05:28:21 AEST 2017


Will Senn writes:
> I am curious about how the Harvard Architecture relates to Unix, 
> historically. If the Harvard Architecture is predicated on the 
> separation of code from data in order to prevent self-modifying code (my 
> interpretation), then it would seem to me to be somewhat at odds with a 
> Unix philosophy of extreme abstraction (code, data, it's all 0's and 
> 1's, after all). In my naive understanding, the PDP-11 itself, with the 
> Unibus and apparently agnostic ISA seem to summarily reject the Harvard 
> Architecure...
> 
> My question is - was there tension around Harvard and Von Neumann 
> architectures in Unix circles and if so, how was it resolved?
> 
> Thanks,
> 
> Will

I don't know how to answer this question directly but in my opinion the
distinction between von Neumann and Harvard architecture machines became
moot with the introduction of memory management units.  For all intents
and purposes instructions were separate from data from the PDP 11/70 on.

Jon


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