One of the key elements of Enterprise Manager Cloud Control is the Oracle Management Service (OMS), which coordinates with plug-ins and Oracle Management Agents to find targets, manage them, and store the resulting data in a repository for further analysis and reference.
By default, the installer installs one OMS and one Management Agent when you initially install Enterprise Manager. While the default configuration works well in smaller environments, you may need to install extra OMS instances in larger production systems to assist ease the burden on a single OMS and boost data flow efficiency.