It’s not well known (but is becoming better known) that the NES’s PPU graphics chip has an unutilized feature. It has a way to pipe graphics into it from another PPU, giving the two chips a combined output. The Famicom and NES both ground out the pins that would allow using this interesting feature, making it impossible to use without desoldering and some other changes, but Youtuber decrazyo performed the necessary modifications (5 minutes) and thus made a system capable of hardware parallax scrolling, 128 sprites with up to 16 per scanline, and additional color flexibility.
The existence of this feature implies that the PPU was intended for greater things at some point in its development. A lot of the limitations of classic hardware end up being due to economic and complexity tradeoffs prevalent at the time of their making. I find it intriguing to imagine the PPU’s chip designers anticipating a future where it could have been daisy-chained like this.
