Last Quiz Flashcards
What is a file
Contiguous logical address space
What are the types of data stored in files
Numeric
Character
Binary
What are some attributes of files?
Name
Identifier
Type
Location
Size
Protection
Time, date and user identification
What are some file operations?
Create
Write
Read
Reposition within file, ie seek
Delete
Truncate
Open
Close
What is needed to manage open files?
Open file table
File pointer
File open count
Disk location of the file
Access rights
What is the Open File Tables?
Tracks open files
What is the File Pointer?
Pointer to last read/write location per process that has the file open
What is the File open count?
Counter of number of times a file is open to allow removal of data from open file table when last processes closes
What is the disk location of the file?
The cache of data access information
What is the Access rights?
Per process access mode information
How is file locking implemented?
Use shared locks and exclusive locks similar to reader writer locks
What is the difference between mandatory file locking and advisory file locking?
In mandatory file locking access is denied depending on locks held and requested and advisory processes can find statuses of locks and decided what to do
What are the two usual access methods?
Sequential access, and direct access
In sequential access how is the file read?
Byte by byte in order
In direct access how is the file read?
The pointer shifts to the position specified by the input
What is the entity containing file system known as?
Volume
What does each volume track in the file systems info?
The device directory or the volume table or contents.
What is a directory structure?
A collection of node containing information about all files
A directory structure is organized logically to obtain what?
Efficiency, naming and grouping
How is a single level directory organized?
By having a single directory for all users
How is a two level directory organized?
Each user has a separate directory
How is an acyclic graph directories organized?
By having shared subdirectories and files
What is a File structure?
A logical storage unit and collection of related information
Where does the file system reside on?
Secondary storage
What is the file control block?
A storage structure consisting of information about a file
What is the device driver?
Controls the physical device
What is the layers of the file system?
Application programs->logical file system-> file organization module->basic file system-> I/O control->devices
What do device drivers do?
Manage I/O devices at the I/O control layer
What does the basic file system do?
Converts commands to the device drivers
What does the file organization module do?
Understands files logical addresses and physical blocks
What does the logical file system do?
Manage metadata information
Translates file names into file numbers, file handles, location by maintaining file control blocks.
What is typically held in the File Control Block?
Data blocks, permissions, size, and dates
What are mount tables?
They store file system mounts, mount points, and file system types
What does the directory structure do?
Organizes the files
What does the system wide open file table do?
Contains a copy of the FCB of each file and other info
What is the Per process open file table?
It contains pointers to appropriate entries in the system wide open file table as well as other info
What are the two ways a directory may be implemented?
With a Linear list or with a hash table.
What is the benefits and downsides of implementing a directory with a linear list?
Benefit: simple to implement
Downside: Linear search time (ie time consuming)
What is the benefits and downsides of implementing a directory with a Hash Table?
Benefit: Reduces the search time
Downside: Has to deal with collisions and only useful if the entries are a fixed sized or uses chained overflow method
What are the three allocation methods?
Contiguous, linked, indexed
What are the benefits and downsides of using the contiguous allocation method?
Benefit: Best performance, and simple to implement
Downside: Need to find space on the disk for a file, knowing the file size ahead of time may be difficult, external fragmentation (need a compaction method)
What are the benefits and downsides of using the linked allocation method?
Benefit: No external fragmentation, improves efficiency of space usage
Downside: Unreliable, locating a block can take a while, must still deal with internal fragmentation
What are the benefits and downsides of using the indexed allocation method?
Benefit: Simple, versatile
Downside: Can improve throughput through clustering
What are extent based file systems?
File systems that allocate disk blocks in extents, where an extent is a contiguous block of disks
What is the free space list?
A list that keeps track of available blocks.
What are some ways to recover data from disks?
Consistency checking, backing up and restoring the data from the backup
