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The process classes single and multi are of historical nature. In the past we had jobs in the JobScheduler setup which use these 'process classes_. For reasons of compatibility, these are still included._
The nameless _process class_ is used for all jobs which doesn't have another _process class._
_ So, all jobs together which doesn't have another _process class'' can run simultaneously in max. 30 tasks.
You can increase this value if necessary.
Start jobs on a JobScheduler Agent
You can run a job on a JobScheduler Agent. For this functionality you have to configure a process class.
See here for more information.