FME Engines connect to an FME Server Core and process requests from the Core. Adding FME Engines connected to the Core increases its ability to perform concurrent processing of requests.
The number of licensed FME Engines you can add is limited only by the host's CPU and memory resources which constrain the maximum concurrent request throughput.
By default, FME Server is configured to start two FME Engines, if two licenses are available. If only one license is available, only one FME Engine starts.
To add an FME Engine to an existing FME Server installation, follow the steps in Editing the Process Monitor Configuration. It is applicable to Windows, Linux, and UNIX.