A postal index number or PIN or PIN code is a code in the postal numbering system or postal code used by India Post, the postal administration of India. The code has six digits.The PIN code system was introduced on August 15, in the year 1972 by Shriram Bhikaji Velankar,an additional secretary in the Union Communications Ministry. The system was introduced to simplify manual sorting and mail delivery by eliminating confusion about incorrect addresses, similar place names and various languages used by the public. There are nine PIN zones in India, including eight regional zones and one functional zone. The first digit of PIN code indicates the region.
The second digit will indicates the sub region and the third digit will indicates the classification district within the region.The final three digits are assigned to individual post offices.The first three digits of the PIN represent a specific geographic region called a classification district that is headquartered in the main post office of the largest city and is known as the classification office. A state may have one or more classification districts depending on the volumes of mail handled.The fourth digit represents the route in which a delivery office is located in the classification district. This is 0 for offices in the central area of the classification district.The last two digits represent the delivery office within the classification district from 01, which would be the GPO or HO.http://www.citybusinessinfo.com/blog/post/total-number-of-pincodes-in-india