The COM+ Event System (EventSystem) service provides automatic event distribution to COM components that subscribe to it. COM+ events extend the COM+ programming model to support late-bound events or method calls between the publisher or subscriber and the event system. The event system notifies event consumers as information becomes available, and it does not repeatedly poll the server.

The COM+ Event System service handles most of the event semantics for the publisher and the subscriber. Publishers offer to publish event types, and subscribers request event types from specific publishers. Subscriptions are maintained outside the publisher and the subscriber, and they are retrieved when needed, which simplifies the programming model for both. The subscriber is not required to contain the logic to build subscriptions-it is possible to build a subscriber as easily as a COM component. The life cycle of the subscription is separate from that of the publisher or the subscriber. You can build subscriptions before the subscriber or publisher is activated.

This service is installed by default and its startup type is Automatic. When started in its default configuration it logs on by using the Local Service account. When the COM+ Event System services stops, the System Event Notification service closes and cannot provide logon and logoff notifications. The Volume Shadow Copy Service, which is needed for Windows Backup and backup applications that rely on the Windows Backup API, also requires this service.

The COM+ Event System service is dependent upon the following system components:

• Remote Procedure Call (RPC)
• DCOM Server Process Launcher
• RPC Endpoint Mapper

The following components are dependent upon the COM+ Event System service:

• Background Intelligent Transfer Service
• COM+ System Application
• SPP Notification Service
• System Event Notification Service