@adeebafatima1, In Index Sequential access Method (ISAM), records are stored in order of primary key. This primary key is then used to sort the records. It is efficient to use primary indexing.
For each primary key of the block also called block anchor, an index entry is created in the index record.
Ohh! My Mistake, I was taken 2K as 2000, but it is 211
@set20a8 your question is valid, i too have the same doubt, what if it was multilevel secondary indexig?