some concept of file Systems

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Virtual File System(VFS)
   A virtual file system (VFS) or virtual filesystem switch is an abstraction layer on top of a more concrete file system. The purpose of a VFS is to allow client applications to access different types of concrete file systems in a uniform way. A VFS can, for example, be used to access local and network storage devices transparently without the client application noticing the difference.
   One of the first virtual file system mechanisms in Unix-like systems was introduced by Sun Microsystems in SunOS 2.0 in 1985. It allowed Unix system calls to access local UFS file systems and remote NFS file systems transparently.Other Unix virtual file systems include the File System Switch in System V Release 3, the Generic File System in Ultrix, and the VFS in Linux. In OS/2 and Microsoft Windows, the virtual file system mechanism is called the Installable File System.

Unix File System
The Unix file system (UFS) is a file system used by many Unix and Unix-like operating systems. It is also called the Berkeley Fast File System, the BSD Fast File System or FFS. It is a distant descendant of the original filesystem used by Version 7 Unix.

Network File System (protocol)
    Network File System (NFS) is a network file system protocol originally developed by Sun Microsystems in 1983, allowing a user on a client computer to access files over a network as easily as if the network devices were attached to its local disks. NFS, like many other protocols, builds on the Open Network Computing Remote Procedure Call (ONC RPC) system. The Network File System protocol is specified in RFC 1094, RFC 1813, and RFC 3530 (which obsoletes RFC 3010).
    Though the use of NFS occurs most commonly with Unix-like systems, other software platforms such as the classic Mac OS, Microsoft Windows, Novell NetWare, and IBM AS/400 operating systems can also use the protocol. Alternative remote file access protocols include the Server Message Block (SMB, also known as CIFS) protocol, Apple Filing Protocol (AFP), NetWare Core Protocol (NCP), and OS/400 File Server file system (QFileSvr.400). SMB and NetWare Core Protocol (NCP) occur more commonly than NFS on systems running Microsoft Windows; AFP occurs more commonly than NFS in Macintosh systems; and QFileSvr.400 occurs more commonly in AS/400 systems.