I'm new to php.  Got the following error when trying to open a DBM: Installation of PHP was with the defaults, is there some additional SW that will allow DBM?

Fatal error: Call to undefined function: dbmopen() 


//open a DBM database; create if it doesn't exist
$fn =  "/qes/IP4700
# $dbh = dbmopen( "$UserDefinedTSdir", "c" ) or die ( "Couldn't open DBM" );
$dbh = dbmopen( $fn, "c" ) or die ( "Couldn't open DBM" );
dbmclose ($dbh);