The Atrium CMDB is where you would store all your configuration items, whether they're physical or logical. For example, server PCs, routers, switches, and other network devices, as well as the software installed on these servers or devices. It also involves maintaining relationships between these items.
On top of that, you build what we call the service model. You define a service and relate all the CIs to that service. This helps in understanding the organization's service structure and is useful in case of incidents or issues.
On the ITSM side, since CMDB is at the core of ITSM, let's say there's an incident on a certain device. With CMDB, you would know which service is impacted and even which users are impacted. This modeling of the CMDB and CI, along with the actual inventory, extends to what is known as IT asset management or the broader CMDB (Configuration Management Database).