Consider four process all are arriving at time zero, with total execution time of 20, 10, 10 and 20 unit respectively. Each process spends the first 20% of execution time doing CPU, the next 60% of doing I/O computation and the last 20% of time doing CPU computation again. The operating system uses longest time first scheduling algorithm and schedules a new process either when running process get blocked I/O or when the running process finishes its CPU burst. Assume that are I/O operations can be overlapped as much as possible. What is the average completion time of the system (in unit)?
[Note: When same burst occurs for multiple process high priority given to lowest process id] (upto one decimal place)
- 24.5
- 23.5
- 25.5
None of these
MY ANSWER IS 24.