A Comparative Analysis of Disk Scheduling Policies
Five well-known scheduling policies for movable
head disks are compared using the performance 
criteria of expected seek time (system oriented)and expected
waiting time (individual I/O request oriented). 
 Both analytical and simulation results are obtained.
 The variance of waiting time is introduced as 
another meaningful measure of performance, showing possible
discrimination against individual requests. 
 Then the choice of a utility function to measure total
performance including system oriented and individual 
request oriented measures is described.  Such a function
allows one to differentiate among the scheduling 
policies over a wide range of input loading conditions.
 The selection and implementation of a maximum 
performance two-policy algorithm are discussed.
CACM March, 1972
Teorey, T. J.
Pinkerton, T. B.
