Questions and Answers
What is the main purpose of a file system?
managing information on secondary storage
What are some common file attributes? Select all that apply.
Size
What are some advantages of indexed allocation?
Small internal fragmentation, easy sequential and direct access
Files are intended to be non-volatile and can be easily copied from one place to another. Is this statement true or false?
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Match the file allocation techniques with their descriptions:
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What are some disadvantages of indexed allocation?
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Sequential access reads one record after ____________.
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What permissions can be granted in Windows for a file?
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The command ls -l is used to show __________ permissions of files.
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The chmod command is used to change file permissions in UNIX/Linux.
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Study Notes
File System Concepts
- Secondary storage is a non-volatile repository for data and programs.
- File systems manage information on secondary storage, providing a mapping between logical and physical views of a file.
- A file system provides services such as keeping track of files, I/O support, secondary storage management, I/O device sharing, and protection mechanisms.
File Concept
- Files are managed by the operating system, which defines how they are structured, named, accessed, used, protected, and implemented.
- A file is a named collection of related information, seen as a sequence of bytes, with two views: logical (programmer's) and physical (operating system).
- Files are intended to be non-volatile, movable, and accessible by different programs and users.
File Attributes
- File attributes include:
- Name (human-readable form)
- Type (for systems supporting different types)
- Location (pointer to file location on device)
- Size (current file size)
- Protection (controls reading, writing, executing)
- Time, date, and user identification (for protection, security, and usage monitoring)
- File attributes are stored in the directory structure on disk.
File Access Methods
- File access methods include:
- Sequential (in order, one record after another)
- Direct (random, skipping previous records)
- Keyed (in any order, with a particular value)
File Operations
- File operations include:
- Create
- Write
- Read
- File seek (reposition within file)
- Delete
- Truncate
- Open (search the directory structure on disk for entry Fi and move the content of entry to memory)
- Close (move the content of entry Fi in memory to directory structure on disk)
File Organization
- File organization schemes include:
- Sequential
- Indexed-sequential
- Indexed
- Direct (or hashed)
Directories
- A directory is a symbol table that can be searched for information about files.
- A typical directory entry contains information (attributes) about a file.
- Common directory structures include:
- Single-level (flat)
- Two-level
- Tree (hierarchical)
File Allocation
- File allocation schemes include:
- Contiguous (allocate disk space like paged, segmented memory)
- Chained (linked) allocation
- Indexed allocation
- File allocation techniques allocate disk space on a per-block (smallest addressable disk units) basis.
File Permissions
- File permissions include read, write, and execute privileges.
- In Windows, permissions can be changed using the Security tab on a file's Properties dialog box.
- In UNIX/Linux, permissions are set using the chmod command.
- File ownership and group can be changed using the chown and chgrp commands, respectively.
