A memory combination includes a first riser board, a second riser board, a pivotal plate, a first engaging member, and a second engaging member. The first riser board has a first edge and a second edge parallel to each other. The second riser board has a third edge and a fourth edge parallel to each other. The pivotal plate are pivotally connected to the first riser board to be adjacent to the first edge and to the second riser board to be adjacent to the third edge. The first and second engaging members are respectively disposed on the first and second riser boards to be respectively adjacent to the second and fourth edges. When the first and second riser boards rotate to be perpendicular to the pivotal plate, the first engaging member is engaged with the second engaging member.