Q. Characteristics of Magnetic disk?

Tracks and Sectors: Disk is divided in concentric rings known as tracks. Thus a track is one complete rotation of disk underneath read/write head. Every track is subdivided in a number of sectors. Every sector comprises a particular number of bytes or characters. Typical sector capacities are as follows: 128, 256, 512, 1024 and 4096 bytes. 

Bad Blocks: Drive maintains an internal table that holds sectors or tracks that can't be read or written to due to surface imperfections. This table is known as bad block table and is created when disk surface is primarily scanned during a low-level format.

Sector Interleave: It signifies the numbering of sectors located in a track. 1 to 1 interleave has sectors numbered serially 0, 1, 2, 3, 4 etc. Disk drive rotates at a fixed speed of 7200 RPM that means there is a fixed time interval between sectors. A slow computer can report a command to read sector 0 storing it in an internal buffer. When it is doing this the drive makes available sector 1 however computer is still busy storing sector 0. So the computer will now have to wait one full revolution till sector 1 becomes available again. Renumbering the sectors such as 0,8,1,9,2,10,3,11 etc gives a 2:1 interleave. It means that sectors are alternated giving the computer a little more time to store sectors internally than previously.