The Kanerva Sparse Distributed Memory (SDM) is a mechanism for implementing a memory with a huge address space. The physical memory consists of substantially fewer locations than the virtual address space. In earlier implemen- tations of the SDM memory the addresses of all physical locations had to be scanned to determine which locations to activate. This is time-consuming, and massive parallel hardware support is needed for other than small appli- cations. This paper introduces a new mechanism for finding the active locations. Using this access mechanism, the access time may be speeded up several orders of magnitude.