From: jl@glen--canyon.com   
      
   On Thu, 12 Feb 2026 23:39:37 +0100, Lasse Langwadt    
   wrote:   
      
   >On 2/12/26 23:12, john larkin wrote:   
   >> On Thu, 12 Feb 2026 21:05:53 +0100, Lasse Langwadt    
   >> wrote:   
   >>   
   >>> On 2/12/26 19:19, john larkin wrote:   
   >>>> The internal stack-oriented architecture of Focal-8 inspired the cool   
   >>>> PDP-11 architecture which in turn inspired the 68K.   
   >>>   
   >>> how did stack-oriented inspire architectures with lots of orthogonal   
   >>> registers, by showing how it should not be done?   
   >>>   
   >>   
   >> Stack-oriented inspired stack-oriented. In the PDP-11, any of the   
   >> registers could be used as a stack pointer.   
   >   
   >so it had a bunch of orthogonal registers that could be used for   
   >anything you like, including stack pointer(s) though I don't see   
   >why you wouldn't always use R6   
   >   
   >that is register oriented, stack oriented is things like Forth and Java   
      
   R6 was used as the sp for JSR, jump subroutine, calls. And R7 was the   
   program counter. But all opcodes worked on all registers, and any reg   
   could be used as a stack pointer or an index register.   
      
   The PDP-11 architecture inspired c, for better or for worse.   
      
   DEC did a lot of ugly hairball async logic back when, delay lines and   
   RCs and such. The first 11 was two boards full of TTL nastiness. There   
   was a short paper-tape reader program that would tease a metastability   
   and hang up the CPU logic in a few seconds.   
      
      
   John Larkin   
   Highland Tech Glen Canyon Design Center   
   Lunatic Fringe Electronics   
      
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