A cluster
placement group is a logical grouping of instances within a
single Availability Zone that benefit from low network latency, high
network throughput. A spread
placement group places instances on
distinct hardware. A partition
placement group places groups of
instances in different partitions, where instances in one partition do
not share the same hardware with instances in another partition.
For more information, see Placement Groups
in the Amazon Elastic Compute Cloud User Guide.