Computer Scheduling

There are many different strategies used for scheduling in computers.  This section examines a simple strategy, with no allowance for process prioritisation, this is the Batch Processing algorithm, and has the following properties: The model can be considered as an M/G/1 case.

It is clear that the average response time of the system for a process that takes x seconds to complete, T(x), will be the time spent waiting in the queue, plus the time to complete the process:

Finding the time to complete

For an M/G/1 queue:

Finding the Waiting Time
Notice how the wait time is totally independent of the job's length, thus batch processing is completely indiscriminate of job length, but this does have the disadvantage that short jobs get no priority and thus batch processing isn't suitable for a time shared system.  From the above we can substitute in W0 to give:
Finding the time to complete

Henry Morgan, 13 June 1999