In [[IBM mainframe]]s, '''Workload Manager''' ('''WLM''') is a base component of [[MVS/ESA]] mainframe [[operating system]], and its successors up to and including [[z/OS]]. It controls the access to system resources for the work executing on z/OS based on user adminstrator-defined goals. Workload Manager components also exist for other operating systems. For example an '''IBM Workload Manager''' is also a software product for [[AIX operating system]].
== z/OS Workload Manager ==
On a mainframe computer many different applications execute at the same time. The expectationexpectations for theexecuting work which executes isare consistent execution times and predictable access to databases. On [[z/OS]] the component Workload Manager (WLM) component fulfills these needs by controlling thework's access to the system resources of the work based on external specifications by the system administrator of the system.
The system administrator '''classifies the''' work to '''service classes'''. The classification mechanism uses work attributes like transaction names, user identifications or program names which are known to thespecific applications are known to use. In addition the system administrator defines '''goals''' and '''importance levels''' for the service classes which representrepresenting the application work. The goals define userperformance expectationexpectations for the work. andGoals can be expressed as '''response times;''', a relative speed (termed '''velocity''') or as '''discretionary''' if no specific requirement exists. The response time describes the duration for the work requests after they entered the system and until the application signals to WLM that the execution is completed. WLM is now interested to assure that the average response time of a set of work requests ends in the expected time or that a percentage of work requests fulfill the expectations of the end user.
The definition of a response time also requires that the applications communicate with WLM. If this is not possible a relative speed measure – named execution velocity - is used to describe the end user expectation to the system.
