  In this paper, we consider systems that can be modelled by $M \mid M \mid n$
queues with heterogeneous servers and non informed customers. Considering any
two servers: we show that the probability that the fastest server is busy is
smaller than the probability that the slowest server is busy. Moreover, we show
that the effective rate of service done by the fastest server is larger than
effective rate of service done by the slowest server.
