Patent US 5,307,461

An extended, hierarchical storage system includes a main storage, an extended storage, and a work storage having a speed and capacity intermediate therebetween, Additionally, a relatively small, high-speed buffer storage is provided as an adjunct to a processor. The work storage implements a store-in mode and incorporates a flag representative of validity of data therein, which, in turn, impacts upon whether an update to lower ranking memory is necessary upon removal of data stored therein.