Unit 5 Device Management
INDEX
Overview
5.1.Device Management Function
5.2.Device Characteristics
5.3.Disk space Management
5.4.Allocation and Disk Scheduling Methods.
Device Management Function in Operating System.
Introduction.
Device management is a key function of an operating system (OS) that handles the control, allocation, and communication of hardware devices.
It ensures that input/output (I/O) devices such as keyboards, printers, hard drives, and network adapters function efficiently.
The OS acts as an interface between the system hardware and users, ensuring smooth interaction between devices and applications.
1. Importance of Device Management
Efficient Utilization of Hardware: Optimizes device usage and prevents conflicts.
Resource Allocation: Manages multiple devices simultaneously.
Error Handling: Detects and resolves hardware-related errors.
Security and Access Control: Restricts unauthorized access to devices.
Device Communication: Facilitates data exchange between hardware components.
2. Functions of Device Management
2.1 Device Detection and Initialization
The OS detects all connected hardware devices during startup.
It loads the necessary drivers to enable communication with these devices.
Plug-and-play mechanisms help recognize new devices automatically.
2.2 Device Drivers and Communication
Device drivers act as intermediaries between the OS and hardware.
The OS loads drivers dynamically as needed.
It ensures that applications interact with devices without needing direct hardware control.
2.3 Resource Allocation and Scheduling
The OS assigns devices to different processes based on priority.
It uses scheduling algorithms to manage multiple devices efficiently.
It prevents resource conflicts by ensuring that only one process accesses a device at a time.
2.4 Buffering and Caching
Buffering temporarily stores data before transferring it between devices.
Caching improves performance by keeping frequently accessed data in memory.
These techniques reduce the impact of slow I/O operations.
2.5 Device Access Control and Security
The OS enforces access policies to ensure that only authorized users or processes interact with devices.
Permissions and authentication mechanisms prevent unauthorized device usage.
It logs device activity for monitoring and security purposes.
2.6 Error Detection and Handling
The OS monitors devices for errors such as hardware failures or connection issues.
It provides error messages and attempts automatic recovery or user notifications.
Faulty devices are isolated to prevent system crashes.
3. Types of Devices Managed by OS
3.1 Input Devices
Keyboards, mice, scanners, touchscreens.
The OS translates user input into commands for applications.
3.2 Output Devices
Monitors, printers, speakers.
The OS manages display settings, print queues, and audio output.
3.3 Storage Devices
Hard drives, SSDs, USB drives.
The OS handles file storage, retrieval, and disk management.
3.4 Network Devices
Network adapters, routers, modems.
The OS controls data transmission between devices and networks.
3.5 Peripheral Devices
External hard drives, webcams, gaming controllers.
The OS ensures compatibility and manages their functions.
4. Device Management Techniques
4.1 Dedicated Device Management
A device is assigned to a single process until it is released.
Used for devices that cannot be shared (e.g., printers).
4.2 Shared Device Management
Multiple processes access a device simultaneously.
The OS uses scheduling algorithms to manage requests (e.g., hard drives, network devices).
4.3 Virtual Device Management
Creates virtual instances of physical devices for efficient sharing.
Examples include virtual printers and disk partitions.
5. Device Management in Different Operating Systems
5.1 Windows OS
Uses Device Manager to manage hardware components.
Supports Plug and Play for automatic device detection.
Provides driver updates and troubleshooting options.
5.2 Linux OS
Uses the
/dev/directory to represent devices as files.Device drivers are loaded as kernel modules (
lsmod,modprobe).udevmanages dynamic device detection.
Device Characteristics in Operating System.
Introduction.
Devices in an operating system (OS) are categorized based on their functionality, speed, and communication methods.
The OS manages these devices by controlling their interaction with applications and ensuring efficient resource allocation.
Understanding device characteristics helps in optimizing system performance and selecting appropriate device management techniques.
1. Classification of Devices
Devices can be broadly classified into three categories based on their characteristics:
1.1 Character Devices
These devices handle data as a continuous stream of characters.
They do not have a structured data format, meaning data is read and written sequentially.
Examples: Keyboards, mice, serial ports, and terminals.
1.2 Block Devices
These devices store and transfer data in fixed-size blocks.
They support random access, meaning data can be read or written in any order.
Examples: Hard drives, SSDs, USB drives, and memory cards.
1.3 Network Devices
These devices facilitate communication between computers over a network.
The OS manages data transmission and reception to ensure smooth connectivity.
Examples: Network interface cards (NICs), routers, and modems.
2. Characteristics of Devices
2.1 Speed Variation
Different devices operate at different speeds.
High-speed devices like SSDs and RAM operate faster, while low-speed devices like mechanical hard drives and printers function slower.
The OS optimizes data transfer rates using buffering and caching techniques.
2.2 Shared vs. Dedicated Devices
Shared Devices: Used by multiple processes or users simultaneously (e.g., hard drives, network devices).
Dedicated Devices: Assigned to a single process at a time (e.g., printers, scanners).
2.3 Sequential vs. Random Access
Sequential Access: Data is read in a specific order (e.g., tape drives).
Random Access: Data can be accessed in any order (e.g., hard drives, RAM).
2.4 Volatile vs. Non-Volatile Storage
Volatile Storage: Data is lost when power is turned off (e.g., RAM).
Non-Volatile Storage: Data is retained even after the system is powered off (e.g., hard drives, SSDs, USB drives).
2.5 Input vs. Output vs. I/O Devices
Input Devices: Send data to the system (e.g., keyboards, mice, scanners).
Output Devices: Receive data from the system (e.g., monitors, printers, speakers).
I/O Devices: Perform both input and output operations (e.g., touchscreen devices, external storage).
2.6 Device Dependency on Software (Drivers)
Devices require software drivers to communicate with the OS.
The OS loads the necessary drivers to ensure proper functionality.
Examples: Printer drivers, graphics card drivers.
2.7 Interrupt-Driven vs. Polling Mechanisms
Interrupt-Driven Devices: Notify the CPU when they need attention (e.g., keyboards, network devices).
Polling Devices: The OS continuously checks if the device needs service (e.g., older printers).
2.8 Plug and Play (PnP) Capability
Some devices support automatic detection and configuration by the OS.
Examples: USB devices, external hard drives.
3. Device Management Techniques Based on Characteristics
The OS applies different management techniques based on device characteristics:
3.1 Buffering and Caching
Used for devices with slower data transfer speeds.
Stores temporary data to improve performance.
Example: Print spooler stores print jobs before sending them to the printer.
3.2 Scheduling and Prioritization
The OS schedules access to shared devices based on priority.
Example: Disk scheduling algorithms like FCFS (First Come First Serve) and SSTF (Shortest Seek Time First) manage multiple disk requests.
3.3 Error Handling and Recovery
The OS detects and corrects device errors.
Example: Bad sector management in hard drives.
3.4 Security and Access Control
The OS enforces permissions to restrict unauthorized access.
Example: File access control lists (ACLs) on storage devices.
4. Device Characteristics in Different Operating Systems
4.1 Windows OS
Uses Device Manager to manage and configure hardware.
Supports Plug and Play for automatic detection.
Provides drivers and updates for various hardware components.
4.2 Linux OS
Represents devices as files in the
/dev/directory.Uses the udev system for device detection.
Supports modular device drivers for better flexibility.
Disk Space Management in Operating System.
Introduction.
Disk space management is a crucial function of an operating system (OS) that ensures efficient storage, organization, and retrieval of data on disk drives.
The OS manages the allocation of disk space, keeps track of free and occupied space, and optimizes disk utilization to enhance system performance.
Proper disk space management helps in preventing fragmentation, reducing access time, and ensuring smooth data storage operations.
1. Importance of Disk Space Management
Efficient Utilization: Maximizes available storage space.
Faster Access: Reduces seek time for data retrieval.
Prevention of Fragmentation: Ensures continuous storage allocation.
Security and Integrity: Protects data from loss or corruption.
File System Maintenance: Organizes files efficiently for smooth operations.
2. Key Components of Disk Space Management
2.1 Disk Partitioning
The process of dividing a physical disk into logical sections.
Each partition acts as an independent storage unit.
Common partition types:
Primary Partition: Can hold the OS and boot files.
Extended Partition: Can contain multiple logical partitions.
Logical Partition: Subdivisions within an extended partition.
2.2 File System Management
The OS organizes data using file systems like FAT32, NTFS, ext4, HFS+.
File systems provide structure for storing, accessing, and managing files.
2.3 Free Space Management
The OS keeps track of free and occupied disk space to allocate efficiently.
Methods used:
Bitmaps: A map of bits where each bit represents a block’s availability.
Linked Lists: A chain of free disk blocks.
Grouping: Groups of free blocks stored together for quick allocation.
2.4 Disk Quotas
Used to limit the disk space usage per user or process.
Prevents excessive disk consumption by a single user.
2.5 Disk Caching
Frequently accessed data is stored in memory to speed up access.
Reduces the number of disk reads and writes.
3. Disk Space Allocation Methods
3.1 Contiguous Allocation
Files are stored in continuous blocks of memory.
Advantages:
Fast access time.
Simple implementation.
Disadvantages:
Leads to fragmentation.
Difficult to resize files.
3.2 Linked Allocation
Files are stored as linked blocks on the disk.
Each block contains a pointer to the next block.
Advantages:
No external fragmentation.
Efficient use of disk space.
Disadvantages:
Slower access time due to pointer traversal.
3.3 Indexed Allocation
An index table stores pointers to file blocks.
Advantages:
Supports direct access.
Reduces fragmentation.
Disadvantages:
Requires additional space for index tables.
4. Disk Space Management Techniques
4.1 Defragmentation
Rearranges fragmented files to store them contiguously.
Improves disk access speed and efficiency.
4.2 Garbage Collection
Removes unused and temporary files to free up space.
Improves storage efficiency and system performance.
4.3 Compression
Reduces the size of files to save disk space.
Used in file systems and data storage solutions.
4.4 Backup and Recovery
Creates copies of important data to prevent loss.
Uses techniques like full backup, incremental backup, and differential backup.
5. Disk Space Management in Different Operating Systems
5.1 Windows OS
Uses tools like Disk Management and Disk Cleanup.
Supports NTFS and FAT32 file systems.
Offers automatic defragmentation to optimize performance.
5.2 Linux OS
Uses the
/dev/directory to manage disk partitions.File systems like ext4, XFS, and Btrfs provide efficient space management.
Commands like
df,du, andfsckhelp monitor and manage disk space.
Allocation and Disk Scheduling Methods.
Introduction.
Efficient disk management is crucial for optimizing system performance.
The operating system (OS) handles disk space allocation and scheduling to ensure smooth data storage and retrieval.
Allocation methods define how files are stored on the disk, while disk scheduling methods determine the order in which disk access requests are processed.
Proper allocation and scheduling improve disk utilization, reduce access time, and enhance system efficiency.
1. Disk Space Allocation Methods
Disk space allocation refers to the way an OS assigns disk blocks to files.
Different methods impact storage efficiency, access speed, and fragmentation.
1.1 Contiguous Allocation
Each file is stored in a continuous block of disk space.
The OS maintains the starting block and length of the file.
Advantages:
✔ Fast access due to sequential storage.
✔ Simple implementation.
Disadvantages:
✘ Causes external fragmentation.
✘ Difficult to expand files if adjacent space is occupied.
1.2 Linked Allocation
Each file is stored as a linked list of disk blocks.
Every block contains a pointer to the next block in the file.
Advantages:
✔ No external fragmentation.
✔ Easy file expansion.
Disadvantages:
✘ Slower access due to pointer traversal.
✘ Extra space required for storing pointers.
1.3 Indexed Allocation
An index table stores pointers to all blocks of a file.
Each file has an index block containing addresses of its data blocks.
Advantages:
✔ Supports direct access.
✔ Reduces fragmentation issues.
Disadvantages:
✘ Extra space needed for index tables.
✘ Fixed index size may limit file growth.
1.4 Multilevel Indexed Allocation
Uses multiple levels of index tables to support large files.
Provides flexibility for file size expansion.
Advantages:
✔ Supports very large files efficiently.
✔ Reduces direct access limitations of single-level indexed allocation.
Disadvantages:
✘ Additional overhead due to multiple index levels.
✘ Complexity in implementation.
2. Disk Scheduling Methods
Disk scheduling determines the order in which disk access requests are handled.
Efficient scheduling minimizes seek time, improves throughput, and balances system load.
2.1 First Come First Serve (FCFS)
Requests are processed in the order they arrive.
Advantages:
✔ Simple and fair.
✔ No request starvation.
Disadvantages:
✘ High average seek time.
✘ Inefficient when requests are scattered.
2.2 Shortest Seek Time First (SSTF)
The request closest to the current head position is served next.
Advantages:
✔ Reduces seek time compared to FCFS.
✔ Improves disk efficiency.
Disadvantages:
✘ May cause starvation for far-away requests.
✘ Frequent head movement may lead to wear and tear.
2.3 SCAN (Elevator Algorithm)
The disk head moves in one direction, servicing requests, and then reverses.
Advantages:
✔ Provides fair access to all requests.
✔ Reduces overall seek time.
Disadvantages:
✘ High response time for new requests at the far end.
✘ Not as efficient as some advanced methods.
2.4 C-SCAN (Circular SCAN)
Similar to SCAN but only moves in one direction, then jumps back to the start.
Advantages:
✔ More uniform wait times than SCAN.
✔ Reduces delays for newly arrived requests.
Disadvantages:
✘ Higher overhead due to head reset.
2.5 LOOK and C-LOOK
Variants of SCAN and C-SCAN that move only to the last request instead of reaching the end of the disk.
Advantages:
✔ Reduces unnecessary movement.
✔ More efficient than SCAN and C-SCAN.
Disadvantages:
✘ More complex than basic scheduling algorithms.
2.6 N-Step SCAN
SCAN is divided into smaller request groups.
Each group is processed separately to prevent starvation.
Advantages:
✔ Reduces waiting time for new requests.
✔ Improves request balancing.
Disadvantages:
✘ Complex to implement.
3. Choosing the Right Allocation and Scheduling Methods
The choice of allocation and scheduling depends on system requirements:
| Criteria | Best Allocation Method | Best Scheduling Method |
|---|---|---|
| Small files | Indexed allocation | FCFS or SSTF |
| Large sequential files | Contiguous allocation | SCAN or C-SCAN |
| Random access files | Indexed allocation | LOOK or C-LOOK |
| High system load | Linked allocation | N-Step SCAN |