A solid state semiconductor and magnetic storage device suited for rugged applications. It is about as fast as a slow hard disk and holds its content without power.
It is conceptually a stationary disk with spinning bits. The unit, only a couple of square inches in size, contains a thin film magnetic recording layer. Globular-shaped bubbles (bits) are electromagnetically generated in circular strings inside this layer. In order to read or write the bubbles, they are rotated past the equivalent of a read/write head.
This is a conceptual drawing of how a bubble memory circuit works.