The ATMOS filestore is different from the normal filestore. The ATMOS filestore can be found by running DQL as below,
DQL> select * from dm_atmos_store
The ATMOS filestore can be created from Documentum Administrator. More details can be found in DA guide. Here is the direct link for DA user guide,https://knowledge.opentext.com/knowledge/llisapi.dll/fetch/2001/3551166/27085930/69125280/66201762/69363926/OpenText_Documentum_Administrator_7.3_User_Guide.pdf?nodeid=69351516&vernum=-2
Hope this helps:)
Architect, Consulting Services
If the ATMOS is configured in S3/CAS modes, then Content Server uses the ATMOS plugin to communicate with ATMOS store.
If ATMOS is configured as normal filestore like SAN or NAS mode, then Content Server will use the OS functions to communicate with filestore.