A default group is system-defined collection of hosts and cannot be deleted or edited.
All Hosts group. Contains all managed hosts. Every machine with an installed agent automatically belongs to this group.
Distribution groups. Contains all hosts of a particular distribution and hardware platform. When an Agent registers with the SDS, it is identified by its operating system (specific Linux or Solaris distribution) and assigned to the group of agents with the same distribution and hardware platform.
For example, you install the agent on five Red Hat 8.0 Intel 32-bit machines. The agents rise. In the console you see a group called RH8_IA32 Hosts, and the five machines are listed under it. You install the agent on another five machines with SLES 9 on Power 64-bit. When the agents rise, you see a new group, SLES9_PPC64 Hosts, and it contains the five machines.