1. 
   
   
   
   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. 
   
   
   
   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. 
   
   
   
   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.