Idle

Key Characteristics

• • Resource Availability: An idle resource (e.g., CPU, I/O device, memory block, user session) is online and ready to accept work, but no work is currently assigned or being processed by it.
  • Waiting State: Often implies that a process or task is in a WAIT state, suspended until a specific event occurs, such as I/O completion, a timer expiring, or user input from a terminal.
  • Minimal Resource Consumption: While idle, a resource typically consumes minimal CPU cycles (e.g., a CPU in a dispatchable wait state, or a task waiting on an event), but may still hold allocated memory or other system resources.
  • Monitored by System: z/OS performance monitors like RMF (Resource Measurement Facility) track idle time for various resources (e.g., CPU, channels, devices) to provide insights into system utilization and capacity.
  • Ready for Work: An idle resource or task can typically transition to an active state quickly once the triggering event occurs or work is dispatched to it.

Use Cases

• • TSO/ISPF User Session: A TSO user logged into ISPF but not actively entering commands or interacting with an application is considered idle, waiting for input.
  • CICS Transaction Task: A CICS task that has completed processing a request but is waiting for the next user input from a terminal is in an idle state.
  • CPU Utilization Reporting: Performance reports often show "CPU Idle Time," representing the percentage of time the CPU was not processing any work, indicating available processing capacity.
  • Batch Job Step: A batch job step might become idle if it's waiting for an I/O operation to complete, a resource to be released by another task, or a specific time of day.
  • Unused Devices: A tape drive, disk volume, or printer that is online but not currently allocated to any job or task is considered idle.

Related Concepts