Scheduling response time ($R_i=f_i-a_i$)

The delay from a task's arrival $a_i$ until its first execution $f_i$: $R_i=f_i-a_i$. This measures access to initial CPU service, rather than completion of an entire user request. For C under round-robin scheduling in process scheduling, $R_C=4-2=2$; its scheduling turnaround time is instead $5-2=3$.