Each problem consists of a single input together with parameters specifying, for example, the number of reads and whether postprocessing (PP) should be invoked. A problem is sent across a network to the SAPI server and joins a queue. Queued problems are assigned to workers, which can run in parallel. A worker prepares the problem for the quantum processing unit (QPU), sends it to the QPU queue, receives results, and bundles the results with additional information about the problem (such as runtime information).
The total time for a problem to pass through the system is the service time. Note that service time includes wait time in two queues, which can vary according to the number of problems and workers active at any moment. The QPU handles problems one at a time; the time for one problem to move through the QPU is the QPU access time.
The diagram below provides a simplified view of the computation workflow on a D-Wave system.
More information is available here: Measuring Computation Time