What are different classes of jobs?
The UNIX operating system job scheduler provides three different types of job classes
* Time-share Job Class : This is the default job class and has priority 0 through 59, with 59 being the highest priority. In this job class, each process is assigned a time slice where the time slice specifies the number of CPU clock ticks that a particular task can occupy. Once the process finishes its time slice, the process is placed on the sleep queue, and the priority decreases.
* System Job Class : This class is reserved for system daemon processes. The priority range for the system job class is between 60 and 99. These are of higher priority than the time-share job class. This is to ensure that the system can provide services to the time-share job class processes when system services such as memory, and/or file I/O are requested.
* Real-Time Job Class : This is the highest priority job class and has no time slice. Real-time process priorities range between 100 and 159. This ensures that critical processes always acquire the CPU as soon as the process is scheduled to run. Because there is no time slice the number of context switches is reduced significantly.
