4. Conclusions
In this paper, we have proposed a new external memory DFS algorithm for general grid graphs. Its performance is better than those of the other known algorithms for this class of graphs. It is still an open question as to whether similar I/O-performance can be achieved in respect of directed grid graphs. The problem of I/O-efficiently finding a DFS-tree of several other graph classes (such as bounded treewidth graphs) and of general graphs has remained open for a long time.