It is possible to install multiple versions of ArcInfo Workstation on a given UNIX machine. This requires small system scripts to set the appropriate environment for each.
Create a system script for each version of ArcInfo to run. In each script, set the ArcInfo environment variables, modify the path variables as necessary, and start ArcInfo.
The following Bourne shell script is an example of a script that will set-up the 7.2.1 environment.
export ARCHOME ATHOME ADOCHOME HHHOME PATH LD_LIBRARY_PATH
echo "Using ARCHOME $ARCHOME"... 1>&2
exec $ARCHOME/bin/arc $*