What do you mean by file systems? What are the major difference between file system interfaces and file system implementation? Explain

We have three essential requirements for long-term information storage:

•   It must be possible to store a very large amount of information.
  
•   The information must survive the termination of the process using it.
  
•   Multiple processes must be able to access the information concurrently.
  The usual solution to all these problems is to store information on disks and other external media in units called files. Files are managed by the operating system. How they are structured, named, accessed, used, protected, and implemented are major topics in operating system design. As a whole, that part of the operating system dealing with files is known as the file system.
  File system implementation deals with:
  

•   How files and directories are stored?
  
•   How disk space is managed?
  
•   How to make everything work efficiently and reliably?
  The main objective of file system implementation is:
  

•   To describe the details of implementing local file systems and directory structures
  
•   To describe the implementation of remote file systems
  
•   To discuss block allocation and free-block algorithms and trade-offs
  Different allocation methods are used in file system implementation. Some of the allocation methods are:
  

•   Contiguous allocation
  
•   Linked allocation
  

 Indexed allocation
File system interface provides applications with various system calls and commands such as open, write, read, seek, etc. Since main memory is usually too small, the computer system must provide secondary storage to back up main memory. The file system provides the mechanism for storage of and (multiple) access to both data and programs residing on the disks. Under this we describe following topics:

•   Access method
  
•   Directory structure
  
•   File system mounting
  
•   File sharing
  
•   Protection