Both retrieval effectiveness (how reliably a system returns relevant documents) and execution efficiency (the average time required to search a document collection) of an interactive information retrieval system are very important when discussing the overall usefulness of the system [11]. If a system consistently returns large amounts of irrelevant information, or the user must wait a long time for a search to be performed, the system is less useful than one that quickly returns a higher percentage of relevant information. The retrieval effectiveness of LSI was discussed in Section 2.2. Since LSI++ merely implements the LSI model, its retrieval performance is governed by the effectiveness of the model. However, the execution efficiency is directly influenced by its implementation. LSI++ has proven to be an efficient implementation of the LSI model described in Section 2.2. The following sections describe the performance of both the serial and distributed implementations of LSI++ and compare the performance of LSI++ to the performance of the original Bellcore implementation of LSI.