Chapter 10: File Systems

Question 1

A file system (FS)

Answer 1

has the function to implement the concept of files.

Question 2

A record is a

Answer 2

structure of related data items, possibly of different data types, identified within a file by a record number or a unique key field.

Question 3

An access method is a set of

Answer 3

operations provided by the OS as part of the user interface to access files. The most common access method is sequential.

Question 4

A Seek is generally not necessary for __________ record files

Answer 4

Fixed-length record files. Any record can be accessed by directly specifying the record number.

Question 5

Metadata is information about the format and

Answer 5

organization of a file’s data and is generally stored in a file header

Question 6

A file header is a

Answer 6

portion of the file preceding the actual data and is visible to only the FS itself.

Question 7

The magic number is a short sequence of

Answer 7

characters at the start of the file header, which identifies the file type. The file type, in turn, determines which programs are allowed to access and interpret the file.

Question 8

A file extension is a

Answer 8

sequence of one or more characters following the file name.

Question 9

A file directory (or folder) is a special-purpose file that

Answer 9

records information about other files and possibly other directories. The directory consists of a set of entries, each containing the name of a file followed by other information necessary to access the file.

Question 10

A tree-structured directory hierarchy is a collection of __________ organized such that (1) __________, and (2) __________

Answer 10

A tree-structured directory hierarchy is a collection of directories organized such that (1) every directory points to zero or more files or directories at the next lower level, and (2) every file and directory except the root is pointed to by exactly one parent directory at the next higher level.

Question 11

The root of a tree-structured directory hierarchy is

Answer 11

the highest level directory, which does not have a parent directory.

Question 12

An absolute path name of a file, uniquely identified by an __________, is the __________ leading from __________ to __________

Answer 12

internal ID, f, is the concatenation of the directory and file names leading from the root to the file f.

Question 13

A relative path name is a

Answer 13

concatenation of file names starting with the current directory.

Question 14

Change (Directory Operation)

Answer 14

Change the current working directory to another directory specified by a path name.

Question 15

Create (Directory Operation)

Answer 15

Create a new named directory and a new entry in the current working directory, which points to the new directory.

Question 16

Delete (Directory Operation)

Answer 16

Delete directory d specified by a path name. Delete also all files and directories reachable using any path name starting from d.

Question 17

Move (Directory Operation)

Answer 17

Move a file or directory from one directory to another.

Question 18

Rename (Directory Operation)

Answer 18

Change the name of a file or directory specified by a path name.
List List the file names and optionally other attributes of all files contained in a directory specified by a path name.

Question 19

Find (Directory Operation)

Answer 19

Find a file or directory specified by a name.

Question 20

A directed acyclic directory hierarchy organizes directories such that any directory at a given level may point to zero or more files or other directories at lower levels but also

Answer 20

permits any file or directory to have more than one parent directory.

Question 21

A reference count is a non-negative integer associated with a file f, which indicates

Answer 21

how many directories are pointing to the file.

Question 22

A symbolic link (or shortcut) is a directory entry that

Answer 22

points to a file or directory just like a regular entry but is treated differently with respect to deletion. A delete operation only removes the link but not the file itself.

Question 23

A File control block (FCB) is a

Answer 23

data structure associated with a filename that contains all relevant attributes of the file. FCBs are stored apart from file directories and are pointed to by the corresponding directory entries.

Question 24

In Unix and other OSs an FCB is called an

Answer 24

i-node.

Question 25

The open file table (OFT) is a

Answer 25

data structure that keeps track of all files currently in use to facilitate efficient access to and manipulation of the files.

Question 26

The open file operation prepares a file for

Answer 26

efficient access and manipulation by retrieving relevant file information from the FCB and storing the information in an entry of the OFT. Subsequent accesses to the file then occur via an index into the OFT.

Question 27

A read file operation

Answer 27

copies data from an open file to a specified area in main memory.

Question 28

A write file operation

Answer 28

copies data from an area in main memory to a specified open file. A generic sequential write operation has the form:

write i, m, n

Question 29

A seek operation

Answer 29

moves the current position of an open file to a new specified position. A generic seek operation has the form:

seek i, k

Question 30

The close file operation

Answer 30

reverses the effects of the open operation by saving the current state of the file in the FCB and freeing the OFT entry.

Question 31

A disk block is a

Answer 31

fixed sequence of bytes on the disk, which can only be accessed as a single unit using low-level read-block and write-block operations.

Question 32

In a contiguous block allocation scheme, every file is

Answer 32

mapped into a contiguous sequence of disk blocks. The FCB points to the first disk block. The file length, also maintained in the FCB, determines how many blocks are occupied by the file.

Question 33

With a linked block allocation scheme, the blocks containing a file may be

Answer 33

scattered throughout the disk. The FCB points to the first block and each block points to the logically next block.

Question 34

A clustered block allocation scheme links together sequences of

Answer 34

contiguous blocks. The last block of any cluster points to the beginning of the logically next cluster.

Question 35

A File allocation table (FAT) is an

Answer 35

array where each entry corresponds to a disk block. The FAT keeps track of which disk blocks belong to a file by linking the blocks in a chain of indices.

Question 36

With an indexed block allocation scheme, file blocks may reside

Answer 36

anywhere on the disk. An index table is provided for each file, which keeps track of the blocks belonging to the file.

Question 37

Differences between linked and indexed block allocation scheme

Answer 37

The indexed block allocation scheme provides fast random access to file blocks through an index block, but requires additional overhead for storing and maintaining the index. The linked block allocation scheme allows for dynamic allocation and flexible resizing of files, but may have slower random access due to traversing linked lists and increased disk seek time. The choice between the two schemes depends on factors such as the access patterns, file sizes, and trade-offs between random access performance and space efficiency.

Question 38

A bitmap is a data structure where each bit represents

Answer 38

one disk block. A 1 indicates that the block is allocated and a 0 indicates that the block is free.

Question 39

We can use the virtual memory techniques discussed in Virtual Memory to treat file I/O as routine memory accesses. This approach, known as __________, allows a part of the virtual address space to be logically associated with the file.

Answer 39

memory mapping a file

Question 40

The general outline for creating a region of shared memory using memory-mapped files in the Windows API involves first creating a __________ for the file to be mapped and then establishing a view of the mapped file in a process’s virtual address space.

Answer 40

file mapping

Question 41

To establish a memory-mapped file, a process first opens the file to be mapped with the CreateFile() function, which returns a HANDLE to the opened file. The process then creates a mapping of this file HANDLE using the CreateFileMapping() function. Once the file mapping is done,

Answer 41

the process establishes a view of the mapped file in its virtual address space with the MapViewOfFile() function. The view of the mapped file represents the portion of the file being mapped in the virtual address space of the process—the entire file or only a portion of it may be mapped.

Question 42

The call to CreateFileMapping() creates a

Answer 42

named shared-memory object called SharedObject.