Comment by jhallenworld

CRTs are very forgiving- 512x342 vs x384 would have made very little difference. You could still get square pixels by minor adjustments to vertical and horizontal size.

My question is what is the htotal and vtotal times in pixels and lines? Maybe there was a hardware savings to have vtotal exactly equal to 384 (which is 128 times 3). Perhaps they saved one bit in a counter, which may have resulted in one fewer TTL chip.