Minecraft wiki entry for Memory, associated text: Allows a lot of flexibility in geometry — the droppers can be read from 3 sides each and activated from 5 sides each; can be oriented vertically too and content can be read with comparators through solid blocks. However, always power it through an adjacent block; if players power the dropper directly, they will activate the other dropper too and the order is unpredictable. Activates on rising edge, meaning they can apply S even while R is still active or vice versa.