Copyright 1996 José Carlos Brustoloni and Peter Steenkiste. Published in the Proceedings of OSDI'96, October 28-31, 1996 in Seattle, WA, USA. The authors have granted to the USENIX Association exclusive publication rights for an initial period of twelve months and non-exclusive publication rights thereafter. Copyright to this work is retained by the authors. Permission is granted for the noncommercial reproduction of the complete work for educational or research purposes.