Step 1: Why an index is needed:
An index is a guide that tells where a record is kept in the file. It helps find a paper quickly.
Indexes are of different kinds. Two of them are the book index and the loose leaf index.
Step 2: Book index:
A book index is kept in a bound register or book. Its pages are divided alphabetically, such as A, B, C and so on.
Names of persons or firms are written on the pages in alphabetical order, with the file number against each.
Its good point is that the pages cannot be lost and it is cheap and simple.
Its weak point is that it is not flexible. New names cannot be inserted in the right place, and old entries cannot be taken out.
Step 3: Loose leaf index:
A loose leaf index uses separate sheets held in a binder or a cover with rings or screws.
Sheets can be added, removed or moved to keep the alphabetical order.
Its good point is that it is flexible and can grow. Its weak point is that sheets can be lost or misplaced.
Final Answer:
A book index is entries in a bound book and is permanent but not flexible. A loose leaf index uses separate sheets in a binder and can be changed easily.