p4 is in the public domain and can be obtained by anonymous ftp to info.mcs.anl.gov at Argonne National Laboratory. It is also available through netlib. The distribution contains all the source code, a meta-makefile to build p4 on any of the machines described below, a set of examples, and a User's Guide [5], which can be installed as an on-line help system as well, via the Gnu Emacs info mechanism. It is available for the following set of machines: Sequent Symmetry; Encore Multimax; Alliant FX/8, FX/800, FX/2800, and Campus; Cray X/MP and C-90; workstations from Sun, NeXT, HP, DEC, Silicon Graphics, IBM; Stardent Titan; BBN GP-1000 and TC-2000; Intel iPSC/860, Touchstone Delta, CM-5, and Paragon; nCUBE; KSR; and IBM SP-1 (TCP, EUI, and EUI-H interfaces). It is not difficult to port to new systems, and we intend to do these ports when new machines become available.