Identify the kind of files according to the organization and give a very brief description.

Type of files organization:

Serial :
A collection of records without sequence.The records are stored in the order received.
Sequential:
A collection of records with sequence.Adding/deleting records requires new files.
Indexed Sequential:
The records are stored at known address.The address is calculated by applying a mathematical function to the key field.
Direct Access/Random Access: 
They are stored on a direct access backing storage medium.