[HN Gopher] Xortran - A PDP-11 Neural Network With Backpropagati...
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       Xortran - A PDP-11 Neural Network With Backpropagation in Fortran
       IV
        
       Author : rahen
       Score  : 21 points
       Date   : 2025-11-11 20:10 UTC (2 hours ago)
        
 (HTM) web link (github.com)
 (TXT) w3m dump (github.com)
        
       | jacobgorm wrote:
       | When I studied cognitive psychology I remember one of the
       | professors told us about how they had been playing with
       | implementing neurals nets on their PDP11 back in the day. I
       | remember thinking that had to have been be a total waste of time.
       | Silly me.
        
         | rahen wrote:
         | The first convolutional neural network, the Neocognitron, was
         | AFAIK implemented on a PDP-11 as well:
         | https://www.semanticscholar.org/paper/Neocognitron%3A-A-neur...
         | 
         | No backpropagation back then, this only appeared around 1986
         | with Rumelhart, probably on VAX machines by that time.
         | 
         | The 11/34 was hardly a powerhouse (roughly a turbo XT) but it
         | was sturdy, could handle sustained load and its FPU made the
         | whole difference.
        
           | PaulHoule wrote:
           | If I remember right that FORTRAN IV compiler really sucked,
           | it used a stack machine and that floating point accelerator
           | "sucked" by normal standards but was actually 100% effective
           | at accelerating that stack machine. The FORTRAN 77 compiler
           | that came latter was better.
        
             | rahen wrote:
             | Author here. They call it a FORTRAN IV compiler but it uses
             | some F66 extensions, such as proper types and functions,
             | although it lacks some of the nicer constructs of F66 like
             | If/Then/Else, which would have been handy.
             | 
             | Regarding floating point, I realized the code actually
             | works fine without an FPU, so I assume it uses soft-float.
             | There's no switch to enable the FP11 opcodes, maybe that
             | was in their F77 compiler.
             | 
             | It's indeed rough and spartan, but using a 64KB optimizing
             | compiler requiring just 8KB of memory was a refreshing
             | change for me.
        
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       (page generated 2025-11-11 23:00 UTC)