FILE SYSTEM

1.What are the most common schemes for defining the logical structure of a directory?

The most common schemes for defining the logical structure of a directory

•  Single-Level Directory

•  Two-level Directory

•  Tree-Structured Directories

•  Acyclic-Graph Directories

•  General Graph Directory

2.Define UFD and MFD.

In the two-level directory structure, each user has her own user file directory (UFD). Each UFD has a similar structure, but lists only the files of a single user. When a job starts the system's master file directory (MFD) is searched. The MFD is indexed by the user name or account number, and each entry points to the UFD for that user.

3.What is a path name?

A pathname is the path from the root through all subdirectories to a specified file. In a two-level directory structure a user name and a file name define a path name.

4.What are the various layers of a file system?

The file system is composed of many different levels. Each level in the design uses the feature of the lower levels to create new features for use by higher levels.

•  Application programs

•  Logical file system

•  File-organization module

•  Basic file system

•  I/O control

•  Devices

5.What are the structures used in file-system implementation?

Several on-disk and in-memory structures are used to implement a file system

a.  On-disk structure include

·  Boot control block

·  Partition block

·  Directory structure used to organize the files

·  File control block (FCB)

b.  In-memory structure include

·  In-memory partition table

·  In-memory directory structure

·  System-wide open file table

·  Per-process open table

6.What are the functions of virtual file system (VFS)?

a.   It separates file-system-generic operations from their implementation defining a clean VFS interface. It allows transparent access to different types of file systems mounted locally.

b.   VFS is based on a file representation structure, called a vnode. It contains a numerical value for a network-wide unique file .The kernel maintains one vnode structure for each active file or directory.

7.Define seek time and latency time.

The time taken by the head to move to the appropriate cylinder or track is called seek time. Once the head is at right track, it must wait until the desired block rotates under the read-write head. This delay

is latency time.