**UNIX is a trademark of Bell Laboratories.

This work was done under grants from the National Science Foundation under grant MCS80-05144, and the Defense Advance Research Projects Agency (DoD) under Arpa Order No. 4031 monitored by Naval Electronic System Command under Contract No. N00039-82-C-0235.

**The actual number may vary from system to system, but is usually in the range 5-13.

*** I.e., unmounted and not being written on.