Q. Explain drectory structure with its type , discuss directory implementation?

Q1. explain the folling term with respect to directory –

- two lavel directory structure with diagram,
- tree structured directories with diagram?

-Two level directory : Two-level directory structure contains Master file directory at
the top level then user file directory at the second level, Actual user files are at the
third level.

File system maintains a master block for each user. Master block has one entry for
each user. User directory address is stored in the master block. Each user has a
private directory.

-Tree structured directory = In this structure, directory itself is a file, A directory

and sub directory contains a set of files. Internal format is same for all directories.
Commonly used directory structure is tree Structure. Tree has a root directory. All
files in disk have a unique path name.

3.Single-Level Directory Structure:

In a single-level directory structure, all files are stored in a single directory without any
subdirectories. This structure is simple and straightforward but lacks organization and
scalability. It limits the ability to categorize files or create a meaningful hierarchy.

Acyclic-Graph Directory Structure:

The acyclic-graph directory structure allows directories to be linked or shared, creating a more flexible and
dynamic organization. It allows a directory to be accessed from multiple paths, facilitating efficient file
sharing and reducing storage redundancy.
Q2. what is file managment system? explain file syste implimentation in details -
operating system?
A file management system is a component of an operating system that is responsible for
organizing and managing files on a computer's storage devices. It provides a hierarchical
structure for storing, accessing, and manipulating files and directories
1. File Naming
- Each file is assigned a unique name that allows users and programs to identify and access
it. File names can have restrictions on length, character set, and allowed symbols depending
on the file system.
2. Directory Structure:
- Directories provide a way to organize files into a hierarchical structure. Directories can
contain both files and subdirectories.
- The directory structure is typically implemented as a tree, with a root directory at the top
and subsequent directories branching out. Directories can have parent-child relationships,
enabling navigation and file organization.
- Directories store the names and inode references of files and subdirectories they
contain.
3. Allocation Methods:
- File systems need to allocate and manage space on storage devices to store file data.
Various allocation methods are employed, including contiguous, linked, and indexed
allocation.
- Contiguous allocation assigns a continuous block of space for each file. It provides fast
access but suffers from fragmentation issues when files are deleted or resized..
4. File Access and Permissions:
- File systems enforce access control mechanisms to protect files from unauthorized
access. Permissions are assigned to files and directories, specifying read, write, and execute
rights for the owner, group, and other users.
- Access control lists (ACLs) and file permissions are used to determine who can perform
specific operations on files.
5. File System Operations:
- File system implementations provide various operations to manage files, including
creating, deleting, renaming, moving, and modifying files and directories.
- These operations involve updating the file system's data structures, such as modifying
directory entries, updating metadata, and managing space allocation.
Q3. define following terms with respect to disk accecess-
1) seek time, 2) rotational latency, 3)data transfer time
--- >
1. Seek Time:
Seek time is the time taken by the disk drive's read/write head to position itself over the
desired track on the disk. The seek time includes both the time required for the head to
move to the correct cylinder (called the "seek time") and the time to position itself over the
correct sector on that cylinder (called the "rotational delay" or "rotational positioning
time"). Seek time is typically measured in milliseconds (ms) and is a significant factor
contributing to the overall latency of disk access.

2. Rotational Latency:
Rotational latency, also known as rotational delay or rotational latency time, is the
additional time needed for the desired disk sector to rotate under the read/write head after
the head is positioned over the correct track. This delay occurs because the disk platter
rotates at a constant speed, and the sector being accessed may not be immediately under
the head. Rotational latency is measured in terms of the time taken for one complete
revolution of the disk platter and is typically expressed in milliseconds (ms). It contributes to
the overall time required for a disk read or write operation.

3. Data Transfer Time:

Data transfer time, also known as data access time or data transfer rate, refers to the time
taken to read or write the actual data once the head is positioned correctly on the desired
track and the rotational latency is over. It represents the time required to transfer the data
between the disk and the computer's memory or between different sectors on the disk.
Data transfer time depends on factors such as the disk's rotational speed, the density of
data on the disk, and the disk's interface speed (e.g., SATA or PCIe). It is typically measured
in terms of data transfer rate, such as megabytes per second (MB/s) or gigabytes per second
(GB/s).
Q4. what is free space managment (FSM)? explain how bot vector and linked 1st perform
an FSM ?
--- > 1. Definition: Free space management is a mechanism used by file systems to track and
manage available and allocated space on storage devices.
➢ Bit Vector Method:
1. Allocation Bitmap: A fixed-size array called the "allocation bitmap" or "free space
bitmap" is used.
2. Representation: Each bit in the bitmap corresponds to a specific block on the disk.
3. Allocation: To allocate a block, the file system searches for a free bit in the bitmap and
marks it as allocated (set the corresponding bit to 1).
4. Deallocation: When deallocating a block, the corresponding bit is set to 0, indicating it is
now available for reuse.
5. Efficiency: The bit vector method allows for efficient searching of free blocks with bitwise
operations.
6. Drawbacks: It has a fixed-size nature, limiting the maximum number of blocks that can be
managed. Additionally, the bitmap requires memory space, which can be significant for
large storage devices.
➢ Linked List Method:
1. Linked List Structure: Each storage block contains a pointer to the next free block on the
disk.
2. Allocation: To allocate a block, the file system traverses the linked list, finds a free block,
updates the pointers, and marks it as allocated.
3. Deallocation: When deallocating a block, the block is returned to the free space pool, and
the corresponding pointers are updated to include it in the linked list of free blocks.
4. Flexibility: The linked list method provides flexibility in managing free space without a
fixed-size constraint.
5. Efficiency: While traversing the linked list requires more time compared to the bit vector
method, the linked list method is more space-efficient as it only requires pointers to track
free blocks.
6. Fragmentation: The linked list method may be prone to external fragmentation, where
free blocks are scattered throughout the disk, potentially impacting performance.
Both the bit vector and linked list methods offer approaches to manage free space
efficiently.
Q5. what is advantage of the double buffering scheme over single buffering?
The advantage of the double buffering scheme over single buffering is the ability to perform
concurrent operations
1. Concurrent Read and Write Operations: In double buffering, two buffers are used instead
of one. While one buffer is being read or processed, the other buffer can be used for writing
or receiving new data. This allows for simultaneous read and write operations to occur
independently.
2. Elimination of Synchronization Delays: In single buffering, read and write operations
must be synchronized, meaning that the read process must wait until the write process is
complete before accessing the buffer. This synchronization introduces delays and can result
in idle time for either the reader or writer. With double buffering, there is no need for
synchronization between read and write operations, as they can happen concurrently.
3. Reduced Data Transfer Latency: Double buffering can significantly reduce data transfer
latency. While one buffer is being filled with new data, the other buffer can be processed or
transferred. This overlapping of operations reduces the overall time required for data
transfer.
4. Improved Throughput: By allowing concurrent read and write operations, double
buffering increases the overall throughput of a system. It enables efficient utilization of
system resources and can result in faster data processing or transfer rates.
Q6. what are file acessed method ? explain them in detail?
--- > File access methods refer to the techniques used to read, write, and manipulate data
within files
1. Sequential Access:
Sequential access involves reading or writing data in a sequential manner, from the
beginning of the file to the end or vice versa. In this method, data is accessed in the order it
was stored, and the position within the file is automatically advanced after each read or
write operation. Sequential access is suitable for processing large amounts of data
sequentially,
2. Direct Access:
Direct access, also known as random access, allows data to be accessed directly at any
given position within a file. It uses a file organization technique that allows for direct access
to specific records or blocks of data within the file. Direct access is achieved by utilizing a
logical record number or an offset to determine the location of the desired data. This
method is beneficial when data needs to be retrieved or modified randomly without the
need to sequentially read or write through the entire file.
3. Indexed Sequential Access:
Indexed sequential access combines the characteristics of sequential and direct access
methods. It involves the use of an index structure that provides a mapping between the
logical key values and the physical locations of the data within the file. The index allows for
quick access to specific records based on their key values. Indexed sequential access is
particularly useful when there is a need for frequent direct access to specific records while
still maintaining a sequential processing capability. It strikes a balance between direct access
efficiency and sequential access convenience.
4. Hashed Access:
Hashed access is an access method that utilizes a hashing algorithm to calculate a unique
address or key for each record within a file. The calculated key is used to directly locate the
physical storage location of the data. This method is efficient for large files and offers fast
access to records based on their unique keys. However, hashed access may suffer from
collisions (multiple records having the same hash key), requiring collision resolution
techniques to handle these cases.