Pradeep - I have seen that line many times before but it doesn't answer my question. Is the limit of 50 the maximum number of concurrently running instances OR the maximum number of instance installs?

Twinsoft - The cluster as whole runs 50 instances of sql, each node dependant on spec will run a subset of these instances. To allow each service a failover path to every other node in the cluster each must have an installation of sql engine for that purpose