Using Magnetic Disk instead of Main

In veriication by explicit state enumeration a randomly ac-cessed state table is maintained. In practice, the total main memory available for this state table is a major limiting factor in veriication. We describe a version of the explicit state enumeration veriier Mur' that allows the use of magnetic disk instead of main memory for storing almost all of the state table. The algorithm avoids costly random accesses to disk and amortizes the cost of linearly reading the state table from disk over all states in a given breadth-rst level. The remaining runtime overhead for accessing the disk is greatly reduced by combining the scheme with hash compaction. We show how to do this combination eeciently and analyze the resulting algorithm. In experiments with three complex cache coherence protocols, the new algorithm achieves memory savings factors of one to two orders of magnitude with a runtime overhead of typically only around 15%.