A central directory server (CDS) is a network node that builds and maintains a directory of resources throughout the network. The CDS server provides some similar function to that of a CMC host in a subarea network. While a CMC is a central place for network management information that operates and controls the network, a CDS manages only the directory functions, not the operational and network management functions that a CMC also provides. The purpose of a CDS is to reduce the number of network broadcast searches to no more than one per resource. The CDS is capable of maintaining its directory even when VTAM® is halted and restarted.

VTAM network nodes and end nodes can register their resources with a central directory server, which acts as a focal point for resource location information. When a VTAM end node registers its resources, it can request that resources be registered either to its network node server only, or to both its network node server and the central directory server. Entries in a directory database can be registered, defined, or dynamic.

When a network node receives a search request for a resource for which it does not have location information, the network node first sends a directed search request to a central directory server, if there is one. The central directory server searches for information about the location of the resource in its directory. If it does not find the resource's location, the central directory server searches end nodes in its domain, other central directory servers, and, if necessary, the entire network.

If the resource is still not found, the central directory server notifies the node that originally requested the search that the search is unsuccessful.