Usually each process gets from the queue one file at a time. For example, if a Processing Station runs 3 processes, it will process 3 files from the queue in parallel. The processes on the Station are completely independent of one another: if one process has finished recognizing the file, it returns the result to the Server Manger and immediately gets the next file from the queue, while the other processes may be still processing other files at this time.
By default, the number of processes on each Processing Station is set to N+1, where N is the number of CPU cores on the station. This value is optimal for processing A4 pages that contain mostly text.