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.

 

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. 
   
   
   
   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