This document is about HeNCE, but since HeNCE uses PVM as its execution environment, some explaination of it is in order. PVM  is a set of library routines and control programs that allow distributed programs to be created using either ``C'' or Fortran. Users add calls to PVM routines to otherwise sequential programs to perform tasks such as message passing and process creation.
It is possible to write distributed programs using PVM directly rather than using HeNCE. Indeed many people do since PVM is relatively easy to install and use in comparision to many other message passing distributed computing libraries. PVM documentation is available from the same sources as the PVM software listed above.