Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. In IBM mainframes, 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 administrator-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. On a mainframe computer many different applications execute at the same time. The expectations for executing work are consistent execution times and predictable access to databases. On z/OS the Workload Manager (WLM) component fulfills these needs by controlling work''s access to system resources based on external specifications by the system administrator.