describe advantages and disadvantages of each allocation method for disk space

1.contiguous allocation
advantages：
1):It’s convenient to access.
2):The number of disk seeks required is minimal.
3):The seek time is also minimal.
4):It supports sequential access and direct access.
disadvantages:
1):It should fine space for a new file.
2):dynamic storage-allocation
3):external fragmentation exists.
2.linked allocation
advantages：
1):Improve disk space utilization without external fragmentation.
2):Facilitate the insertion and deletion of files.
3):Conducive to the dynamic expansion of files.disadvantages:
1):Can only be effectively used for sequential access to files.
2):the pointer needs spaces.
3):waste more disk spaces(more disk fragmentation).
4):reliability.If pointer is lost or damaged,bad things will happen.

3.indexed allocation
advantages:
1):no external fragmentation.
2):satisfies the requirements of dynamic file growth,insertion and deletion.
3):can make full use of external storage space.disadvantages:
1):more seek times and seek spaces.
2):Index table itself brings system overhead,such as : internal and external storage
spaces.access time.