clipka wrote:
> BTW, I guess it's possible to build an extremely-reduced-instruction-set 
> computer with just a single instruction: "Move", reading a data word 
> from one memory address and then storing it in another. All you'd have 
> to do would be to map math-op logic to a few dedicated memory locations; 
> e.g. reading from address 0003 might return the sum of the values stored 
> in 0000, 0001, address 0004 might return their difference, address 0005 
> might return the logical AND of memory locations 0000 and 0001, etc. 
> Even the PC might be stored in one particular address, so writing to 
> that would constitute an unconditional jump. A conditional branch could 
> be modeled by reading a status bit, expanding it to all bits of a word 
> (i.e. 0000 or FFFF), computing the logical AND of that mask and one 
> target address, as well as the logical AND of the mask's inverse and the 
> other target address, computing the sum or logical OR of both results, 
> and ultimately writing that value to the PC. (Alternatively a particular 
> bit in a particular memory address could specify whether the next 
> command is to be skipped or not.)
> 
> The Apollo guidance computer actually used such an approach for various 
> mathematical operations.

That's hardcore RISC, man! :-D

-- 
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