explain the features of major scheduling

Question

Explain the Features of Major scheduling algorithms.

The Features of Major scheduling algorithms is given below:

1. FCFS - i.e. First come first served scheduling
2. Shortest Job First scheduling (SJF)
3. Priority scheduling
4. Round robin scheduling

First come first served scheduling-

• Process which request the CPU first is assigned CPU first
• Managed through FIFO queue.
• Average waiting time is usually long
• Non-pre-emptive
• For time-sharing systems, troublesome

Shortest job first (SJF)

• The process that has the smallest CPU burst time gets first
• This increases the waiting time of long processes.
• Problem - difficult to predict the length of subsequent CPU request
• May be non-pre-emptive or be preemptive

Priority

• Highest priority process finds CPU allocation first
• The larger the CPU burst then lowers the priority
• Priority can be explained internally or externally
• Can be non-pre-emptive or preemptive
• Problem-starvation i.e. blocking of process
• Solution-aging - raises the priority

Round robin

• Time quantum from 10 100 millisecond is described
• Processes are seem in circular queue
• CPU allocation is divided between processes accordingly
• Performance depends heavily upon time quantum
• Pre-emptive