1. contiguous allocation

advantages：

• :It’s convenient to access.


• :The number of disk seeks required is minimal.


• :The seek time is also minimal.


• :It supports sequential access and direct access.

disadvantages:

• :It should fine space for a new file.


• :dynamic storage-allocation


• :external fragmentation exists.

2. linked allocation

advantages：

• :Improve disk space utilization without external fragmentation.


• :Facilitate the insertion and deletion of files.


• :Conducive to the dynamic expansion of files.

disadvantages:

• :Can only be effectively used for sequential access to files.


• :the pointer needs spaces.


• :waste more disk spaces(more disk fragmentation).


• :reliability.If pointer is lost or damaged,bad things will happen.

 

3. indexed allocation

advantages:

• :no external fragmentation.


• :satisfies the requirements of dynamic file growth,insertion and deletion.


• :can make full use of external storage space.

 

disadvantages:

• :more seek times and seek spaces.


• :Index table itself brings system overhead,such as : internal and external storage

spaces.access time.