Operating Systems - File Systems

Directories act as symbol tables that map file names to their corresponding file control blocks or locations on the disk.

A File Control Block (FCB) is created or loaded into memory when a file is opened, allowing the system to track its status and metadata.

Systems often maintain an Active Name Table (ANT) and an Active File Table (AFT) to manage files that are currently in use.

ANT stands for Active Name Table, which stores information about the names of files currently active in the system.

AFT stands for Active File Table, which maintains metadata for files that are currently open or in use.

In file systems, a reference count keeps track of the number of hard links or directory entries pointing to a specific file inode. When the reference count drops to zero, the file data can be safely deleted.

The owner is the user who created the file and typically has full control over its permissions.

To improve efficiency, operating systems group disk sectors into larger units called clusters for file allocation.

Clusters are defined as a fixed number of contiguous disk sectors, which serve as the basic unit of space allocation for files.

A group is a collection of users who share common access permissions to specific files or resources.

Interleaving is a technique used to improve disk performance by placing logical blocks in non-contiguous physical sectors to account for controller latency.

In UNIX systems, the kernel is responsible for managing the buffer cache, which stores disk blocks in memory to improve I/O performance. The file system uses these cached blocks, but the management itself is a kernel-level function.

Defective sectors on a storage medium, such as a hard disk, are commonly referred to as bad blocks or bad sectors. These areas are marked by the operating system so that they are not used for data storage.

A file name is the primary identifier used by users and the operating system to uniquely distinguish one file from another within a specific directory. While other attributes like size or owner exist, they are not unique identifiers.

In the context of file system terminology, SFD stands for Symbolic File Directory. This structure is used to map file names to their corresponding file descriptors or locations.

In UNIX, the kernel maintains a portion of memory to cache disk blocks to reduce disk access frequency; this mechanism is specifically called the buffer cache.

Basic File Directories (BFD) are structures that contain the actual file descriptions, such as location, size, and metadata, whereas symbolic directories typically store the mapping of names to these descriptions.

BFD is the standard abbreviation for Basic File Directory, which is a structural component used in file system management to store file metadata.

FCB stands for File Control Block. It is a data structure used by an operating system to store information about a file, including permissions, size, and location on the disk.

Chained allocation is a method where each block contains a pointer to the next block in the file, effectively functioning like a linked list stored on the disk.

A bitmap is a mapping where each bit represents the state of a corresponding resource, such as a block on a disk being free or allocated. It is essentially a string of bits used for tracking.

Blocking is the process of grouping records into blocks for storage. Deblocking is the inverse process, where records are extracted from these blocks after being read from storage.

The File Control Block (FCB) is the specific data structure used by the operating system to maintain metadata and directory entries related to a file.

Symbolic file directories are designed to store the mapping between human-readable file names and the internal file identifiers or pointers used by the system.

Blocking is the process of combining multiple logical records into a single physical block to improve storage efficiency and I/O performance.