OS-CHAP-8-13: File Systems and Memory Management

File Concept

Logical address space for data and programs.

File Types

Includes data, program, text, source, executable.

File Attributes

Metadata describing files, like name and size.

File Identifier

Unique tag for file within the system.

File Location

Pointer indicating file's location on device.

File Size

Current size of the file in bytes.

File Protection

Controls read, write, execute permissions.

Directory Structure

Nodes containing information about all files.

File Operations

Actions like create, read, write, delete files.

Open File Table

Tracks all currently open files in memory.

File Pointer

Indicates last read/write position in file.

File Open Count

Counts how many processes have opened a file.

Disk Location

Cache for file access information on disk.

Access Rights

Permissions for processes accessing a file.

File Locking

Controls concurrent access to files by processes.

Shared Lock

Allows multiple processes to read simultaneously.

Exclusive Lock

Prevents other processes from accessing a file.

Mandatory Locking

Access denied based on existing locks.

Advisory Locking

Processes can check lock status before access.

File Locking Example

Java API example for file locking implementation.

Memory-Mapped Files

Maps file contents directly into memory space.

File Truncation

Reduces file size to zero or specified length.

Repositioning within File

Changing current read/write position using seek.

exclusiveLock

A lock preventing other threads from accessing data.

sharedLock

Allows multiple threads to read data simultaneously.

raf.length()

Returns the length of the file in bytes.

ch.lock()

Method to acquire a lock on a file region.

SHARED

Lock mode allowing concurrent read access.

Shared Lock

Allows multiple processes to read a file concurrently.

Exclusive Lock

Allows only one process to write to a file.

File Structure

Organization of data in a file.

Sequential Access

Read/write operations occur in order.

Direct Access

Access data at a specified location directly.

Relative Block Number

Indicates position of data in a file.

Access Methods

Techniques to read/write data in files.

Index File

A structure for fast data location.

ISAM

Indexed Sequential Access Method for file organization.

Disk Structure

Physical organization of data on a disk.

RAID

Redundant Array of Independent Disks for data protection.

Volume

Entity containing a file system.

File System

Manages how data is stored and retrieved.

Directory Operations

Functions like search, create, delete files.

Single-Level Directory

One directory for all users, causing naming issues.

Two-Level Directory

Separate directories for each user, improving organization.

Tree-Structured Directories

Hierarchical organization of directories and files.

Acyclic-Graph Directories

Directories allowing shared subdirectories and files.

Dangling Pointer

Reference to a deleted file or directory.

Control Characters

Special characters used for formatting files.

File Types

Categorization based on name and extension.

Formatted Document

File with specific structure and layout.

Complex Structures

Files with advanced formatting beyond simple records.

Logical Grouping

Organizing files based on shared properties.

Variable Size Records

Records with varying lengths in storage.

Backpointers

Pointers linking to previous records in a chain.

Daisy Chain Organization

Method of linking records in a sequence.

Entry-Hold-Count Solution

Counts entries to manage directory space.

Directory Entry Type

New classification for storing directory information.

Link

Pointer referencing an existing file.

Resolve the Link

Follow pointer to find the actual file.

General Graph Directory

Directory structure allowing multiple links to files.

Cycle Detection Algorithm

Algorithm to prevent cycles in directory links.

Garbage Collection

Process of reclaiming unused directory entries.

Current Directory

Designated directory for file operations.

cd Command

Changes the current working directory.

Creating a File

Done within the current directory context.

Deleting a Directory

Removes entire subtree rooted by the directory.

File Protection

Control over file access by owner.

Types of Access

Permissions: read, write, execute, append, delete, list.

Access-Control List

List defining user permissions for file access.

Virtual Memory

Memory management technique using disk space.

Demand Paging

Loading pages into memory on demand.

Copy-on-Write

Technique to delay copying until necessary.

Page Replacement

Algorithm for replacing pages in memory.

Thrashing

Excessive paging causing performance degradation.

Memory-Mapped Files

Files mapped into memory for access.

Allocating Kernel Memory

Managing memory for operating system kernel.

Working Set

Set of pages actively used by a process.

Virtual Memory

Separation of user logical memory from physical memory.

Logical Address Space

View of memory space larger than physical memory.

Physical Memory

Actual memory hardware where data is stored.

Demand Paging

Loading pages into memory only when needed.

Page Frame

Fixed-size block of physical memory.

Memory Management Unit (MMU)

Maps logical addresses to physical addresses.

Concurrent Programs

Multiple programs running simultaneously in memory.

Swapping

Moving processes between physical memory and disk.

Lazy Swapper

Only loads pages when they are required.

Shared Memory

Memory accessible by multiple processes.

Heap

Dynamic memory allocation area growing upwards.

Stack

Memory area for function calls growing downwards.

Holes in Address Space

Unused memory space between stack and heap.

Throughput

Number of processes completed in a given time.

CPU Utilization

Percentage of time CPU is actively processing.

I/O Operations

Input/Output tasks involving data transfer.

Process Creation

Generating new processes in the operating system.

Virtual Address Space

Logical view of how a process is stored.

Error Code

Code indicating an error during program execution.

Unusual Routines

Non-standard code paths in program execution.

Data Structures

Organized formats for storing and managing data.

Demand Segmentation

Loading segments into memory as needed.

MMU Functionality

Memory Management Unit's role in demand paging.