Continuous allocation
Advantage:
(1) sequential access is easy.
(2) fast sequential access.
Disadvantages:
(1) continuous storage space is required.
(2) the length of the document must be known in advance.
Link allocation
Advantage:
(1) improve the utilization rate of external memory space
(2) it is very convenient to add, delete and modify data
Disadvantages:
(1) it cannot support efficient direct access.
(2) fat needs a large memory space.
Index allocation
Advantage:
(1) uniqueness index to ensure the uniqueness of each row of data
(2) greatly speed up data retrieval
(3) connection between accelerometers and meters.
Disadvantages:
(1) it takes time to create and maintain indexes
(2) index occupies a lot of physical space
(3) data addition, deletion and modification need dynamic maintenance to reduce maintenance speed