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23678Re: [midatlanticretro] 50 years of Computer Games

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  • David Gesswein
    Dec 6, 2011
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      On Tue, Dec 06, 2011 at 07:31:07PM -0500, Bill Sudbrink wrote:
      >
      > Porting Space War may be a challenge. The Cromemco version is expecting
      > to run on a 4MHz Z80. I wonder if the 1MHz 6800 is up to the job? How
      > much "umph" does the PDP8 have in comparison? Which kind of display,
      > vector or raster, will take more CPU to drive it? Anybody have any SS-30
      > or SS-50 protoboards for sale/trade?
      >
      The PDP-8/I fastest instruction is 1.5 us. 3 us min for memory access
      instructions. Looks like the minumum 6800 instuction takes 2 cycles
      immediate, 3 cycles for direct address so similar. PDP-8 is 12 bits and
      6800 8 bits so some advantage to PDP-8. 6800 instruction set is
      larger so more efficient (PDP-8 can't subtract, you have to negate
      the value then add). In the end the speed is probably similar.

      The relative speed would depend on how much the graphics board offloads
      of the work. Raster board with sprites or vector board with display lists
      would make CPU load less. Raw raster memory or D/A converters would
      make more work. The PDP-8 control is close to raw D/A converters.

      For a simple display raster is probably less load since it handles the
      refresh for you so you only need to write things that are to be changed.
      Vector without display lists you need to rewrite everything at 30+ Hz to
      prevent flicker.
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