This course is run at the The University of Nottingham within the School of Computer Science & IT. The course is run by Graham Kendall (EMAIL : gxk@cs.nott.ac.uk)
We have previously mentioned that there are two typical types of processes
in a computer system. These are interactive jobs and batch jobs. By their nature
interactive jobs tend to be shorter and batch jobs tend to be longer.
Most companies will try to schedule interactive jobs before batch jobs (at
least during the day) so that the response time to their users and customers
is kept to a minimum.
One way of achieving this is to set up different queues to cater for different
process types.
Each queue may have its own scheduling algorithm. The background queue will typically use the FCFS algorithm, whilst the interactive queue may use the RR algorithm.
Furthermore, the scheduler now has to decide which queue to run (as well as
using the scheduling algorithm with each queue). There are two main methods.
Higher priority queues can be processed until they are empty before the lower
priority queues are executed.
Alternatively, each queue can be given a certain amount of the CPU. Maybe, the interactive queue could be assigned 80% of the CPU, with the batch queue being given 20%.
It should also be noted that there can be many other queues. Many systems will have a system queue. This queue will contain processes that are important to keep the system running. For this reason these processes normally have the highest priority.
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Last Updated : 23/01/2002