Which are the main advantages /disadvantages of the different types of files organization?

ADVANTAGES:

Sequential:
Simple file design. Very efficient when most of the records must be processed or if the data has a natural order . Can be stored on inexpensive devices like magnetic tape.

Indexed Sequential: 
Flexibility and faster than sequential

Direct Access/Random Access: 
Speed of record processing, any record can be directly accessed and concurrent processing is possible.

DISADVANTAGES:

Sequential: 
Overall processing is slow. The entire file must be processed even if a single record is to be searched.

Indexed Sequential: 
Extra storage space for index is required.

Direct Access/Random Access:
More complex than sequential and more backup problems.