Proof: If you move from a random track I to another random track J, the average moving distance is 1/3 of the total disk scan.

Proof: If you move from a random track I to another random track J, the average moving distance is 1/3 of the total disk scan (ignoring the marginal effect caused by a limited number of cylinders)

The question comes from the homework of database system implementation, which is proved by me.

 

Proof: assuming there are L channels, then I, j can be 0, between any one of the L-1. This possible combination has the 2nd power of L.

Therefore, the average moving distance is L/3, that is, sliding L/3 tracks.

 

The blog below this formula will be used. It should be written here first.