# How can OS schedule disk requests efficiently without knowing the LBN to PBN mapping ?

I learn from the OS schoolbook that the OS has the function that schedule the disk requests with the knowing algorithms such as SSTF, SCAN .. However, the date layout inner disk drives now is very complex that we may can't know. Disk zoning, disk skew, disk slipping and many other features of disk drives changes the distribution of data layout. So how can the OS do this work ? Thanks!

While you can't calculate an exact "distance" (in terms of arm movement latency and rotational latency) between two blocks it is approximately the case that if the difference between address $a$ and address $b$ is smaller than the distance between address $a$ and address $c$ then block $a$ will be closer to block $b$ than it is to block $c$.