We propose a parallel directory structure, Fat?Btree,to improve high?speed access for parallel database systems in shared?nothing environments. The Fat?Btree has a three?fold aim: to provide an indexing mechanism for fast retrieval in each processor, to balance the amount of data among distributed disks, and to reduce synchronization costs between processors during update operations. We use a probability?based model to compare the throughput and response time of the Fat?Btree with two ordinary parallel Btree structures, with copies of a whole Btree in each processor, and storing index nodes in a processor. The comparison results indicate that the Fat?Btree is suitable for actual parallel database systems that accept update operations.