Re: [stella] video memory

Subject: Re: [stella] video memory
From: Glenn Saunders <krishna@xxxxxxxxxxxx>
Date: Thu, 11 Sep 1997 23:29:52 -0700 (PDT)

On Fri, 12 Sep 1997, Mike St. Clair wrote:
> Um, somebody *please* correct me if my interpretation is correct, but
> these comments seem to me to say that the ram+rom of a 2600 game is larger
> than the screen buffer/display ram of a modern console.

No, what I'm saying is this:

The 2600 can't really do much thinking when it is generating the display
(well, a little, but not much).  It has to decide what to do on the next
frame mostly during the unused portion of the display, or the vertical
blank interval.

So for all intents and purposes, the 6507 hand-feeds the TIA chip during
the visual portion of the display, and any data that it needs could be
considered "video memory" since the machine is concerned totally with
generating the display, scanline by scanline, during the visual portion of
the code.

Some games require 4, 8K or more worth of data and instructions by the
time that individual screen alone goes from top to bottom.  I'm not
talking about game logic and other game-think.  I'm just talking about
banging the 2600 hardware registers.  So the lack of "video memory" can be

My point is that if the 2600 is generating a very busy display, with many
different sprites and different shapes, and frames of animation, that it
could very well be accessing more "pseudo video memory" if you call it,
than its peers like the Astrocade had built in.  You can not create
complex displays without using more memory than the 2600 provides.  Even
Combat requires more than the 2600's internal scanline buffers to generate
its displays (not much, but some).

The 2600 is a scanline based system (maybe the only one).  It's memory
requirements for the individual scanlines themselves are MINISCULE, and it
requires very modest resources to create simple displays with simple
reflected playfields, but the resources it can require over the course of
a whole screen redraw can be HUGE if you want to make a decent looking
display like Solaris where the screen is filled with nothing but reused
single-line-res sprites with color changes on every scanline with many
frames of animation/scaling.  You can't get something for nothing...

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