Server Naming convention is used because each of the process serving the user requests (Dialogue, BTC, Update, Enqueue, Message, Gateway and Spool DVEBMGS). It is also possible to install and configure all the above servers on different instances or hosts.
Enqueue is used to provide data consistency while updating the system. It provides locks from a lock table before a record gets updated and ensure that the record is available for display during an update.
There will be 1 One Enqueue process installed during installation. It is also possible to increase Enqueue processes to more than one depending upon the updates but most of the customer environments there will be only 1 One enqueue process.
Enqueue process the locks and unlock the record during an update. Enqueue server maintains the lock table on the shared memory of the Central Instance (or on the instance where it is installed).
It is recommended to increase the Enqueue processes only on the Central Instance. Technically the Message and the Enqueue should reside on the same instance (It is not mandatory). If both are installed on the same machine then it will be more comfortable for message server to communicate with Enqueue process to obtain locks for Dialogue process that are coming from other instances.