This way of z/OS Workload Manager controlling the access of work to system resources is named goal oriented workload management and is in contrast to resource entitlement based workload management which defines a much more static relationship how work can access the system resources. Resource entitlement based workload management is found on larger UNIX operating systems for example. A major difference to workload management components on other operating systems is the close cooperation between z/OS Workload Manager and the major applications; middleware and subsystems executing on z/OS. WLM offers interfaces which allow the subsystems to tell WLM when a unit of work starts and ends in the system and to pass classification attributes which can be used by the system administrator to classify the work on the system. In addition WLM offers interfaces which allow load balancing components to place work requests on the best suited system in a parallel sysplex cluster. Additional instrumentation exists which helps database and resource managers to signal contention situations to WLM so that WLM can help the delayed work by promoting the holder of resource locks and latches. Over time z/OS Workload Manager became the central control component for all performance related aspects in a z/OS operating system. In a Parallel Sysplex cluster the z/OS Workload Manager components work together to provide a single image view for the executing applications on the cluster. On a System z with multiple virtual partitions z/OS WLM allows to interoperate with the LPAR Hypervisor to influence the weighting of the z/OS partitions and to control the amount of CPU capacity which can be consumed by the logical partitions. Literature Paola Bari et al.: System Programmer's Guide to: Workload Management. IBM Redbook, SG24-6472 External links Official z/OS WLM Homepage See also Unit Control Block, for a description how WLM controls dynamic Parallel Access Volumes (PAVs) IBM mainframe operating systems