EOS is a disk-based, low-latency storage service. Having a highly-scalable hierarchical namespace, and with data access possible by the XROOT protocol, it was initially used for physics data storage. Today, EOS provides storage for both physics and user use cases. Instances of EOS include EOSUSER, EOSPUBLIC, EOSATLAS, EOSCMS.
The main target area for the service is physics data analysis, which is characterised by many concurrent users, a significant fraction of random data access and a large file-open rate.
For user authentication EOS supports Kerberos (for local access) and X.509 certificates for grid access. To ease experiment workflow integration SRM as well as gridftp access are provided. EOS further supports the XROOT third-party copy mechanism from/to other XROOT enabled storage services at CERN.