Disks provide the bulk of secondary storage for modern computers. Modern disk drives are addressed as large one dimensional arrays of logical blocks, where the block is the smallest unit of transfer. The size of block is usually 512 bytes.

The one dimensional array of logical blocks is mapped onto the sectors of the disk sequentially. Sector 0 is the first sector of the first track on the outermost cylinder.

The no. of sectors per track has been increasing as disk technology improves, and it is common to have more than 100 sectors per track in the outer zone of a disk.

Disk Scheduling
One of the responsibilities of the operating system is to use hardware efficiently. For the disk drives, this means having a fast access time and disk bandwidth. The access time has two major components. The Seek Time is the time for the disk arm to move the heads to the cylinder containing the desired sector. The rotational latency is the additional time waiting for the disk to rotate the desired sector to the disk head.

We can improve both the access time and the bandwidth by Scheduling the servicing of I/O requests in a good order.

Various Disk Scheduling Algorithms,
1.FCFS
   The requests for cynders are processed as they come in.

2.SSTF
  Shortest Seek Time First algorithm processes the request which are nearer to the current cynder in the request queue.

3.SCAN
  In SCAN algorithm, the disk arm moves from one side to the other, and processes the requests while moving.C-SCAN,LOOK,C-LOOk are SCAN type algorithms.

My Applications demonstrates all the above shcedulings with a neat graphical look and a analysis for the best algorithm and much more.