Each service integration server or cluster bus member contains a component called a messaging engine that processes messaging send and receive requests and that can host destinations.
When you add an application server or a server cluster as a bus member, a messaging engine is automatically created for this new member. If you add the same server as a member of multiple buses, the server is associated with multiple messaging engines (one messaging engine for each bus). If the bus member is a WebSphere® MQ server, it does not have a messaging engine, but it lets you access WebSphere MQ queues directly from WebSphere MQ queue managers and (for WebSphere MQ for z/OS®) queue-sharing groups.
To host queue-type destinations, the messaging engine includes a message store where, if necessary, it can hold messages until consuming applications are ready to receive them, or preserve messages in case the messaging engine fails. There are two types of message store, file store and data store. For further information, see Administering message stores.