Viharas were for the purpose of living, Chaityas were assemblies for the purpose of discussions. Further, Chaityas were with Stupas, Viharas did not have stupas.
Sabha or Mahasabha during the Chola empie referred to the exclusive assembly of Brahmans/gatherings of the adult male members in the agraharas, that is, the rent free brahmadeya villages. These assemblies enjoyed a large measure of autonomy.
EXAMIANS