A CIM_Cluster is composed of two or more computer system's, operating together. A computer system may participate in multiple ...

A CIM_Cluster is composed of two or more computer system's, operating together. A computer system may participate in multiple clusters. 

When first establishing or bringing up a cluster, only one computer system may be defined as participating in it. Therefore, the cardinality of the association for the CIM_ComputerSystem reference is Min(1).