Solid rocket motors aren't binary, they just can't be dynamically throttled(early KSP was wrong).
In SRMs, usually a hole is left in the center so that the entire length burns towards inside-out rather than bottom-top so to avoid shifting center of gravity, and the shape of the hole is chosen so change in circumference length matches desired thrust profile. This usually means a star shape; the total lengths of edges in the star is longer than what with a simple circular hole, but the points erode faster and decreases reaction surface.
I think the more useful visualization is that a rocket flies at constant dv^2/dt ~ 1.4, with velocity following an exponential. The first derivative being constant satisfies the criteria for an exponential something.
In SRMs, usually a hole is left in the center so that the entire length burns towards inside-out rather than bottom-top so to avoid shifting center of gravity, and the shape of the hole is chosen so change in circumference length matches desired thrust profile. This usually means a star shape; the total lengths of edges in the star is longer than what with a simple circular hole, but the points erode faster and decreases reaction surface.
I think the more useful visualization is that a rocket flies at constant dv^2/dt ~ 1.4, with velocity following an exponential. The first derivative being constant satisfies the criteria for an exponential something.