Operating Systems Cheatsheet - Part 2

9. Process Scheduling Algorithms

Round Robin (RR)

• Description: Each process is assigned a fixed time in cyclic order.
• Advantages: Fairness, prevents starvation.
• Disadvantages: Poor performance for long tasks.

Shortest Job Next (SJN) / Shortest Job First (SJF)

• Description: The process with the smallest execution time is selected next.
• Advantages: Minimizes average waiting time.
• Disadvantages: Requires knowledge of process execution times.

Priority Scheduling

• Description: Processes are assigned priorities, and the highest priority process is selected next.
• Advantages: Allows for different levels of importance.
• Disadvantages: Starvation of low-priority processes.

10. Memory Management Techniques

Paging

• Description: Divides memory into fixed-size blocks (pages) and processes into blocks of the same size.
• Advantages: Simplifies memory allocation.
• Disadvantages: Fragmentation.

Segmentation

• Description: Divides memory into segments based on logical units such as code, data, and stack.
• Advantages: Supports dynamic memory allocation.
• Disadvantages: Fragmentation.

Demand Paging

• Description: Only loads pages into memory when needed.
• Advantages: Reduces memory wastage.
• Disadvantages: Increased overhead.

11. File System Types

FAT (File Allocation Table)

• Description: Uses a table to map clusters to files.
• Advantages: Simple and widely supported.
• Disadvantages: Limited file size and fragmentation.

NTFS (New Technology File System)

• Description: Journaling file system with improved performance, reliability, and security.
• Advantages: Supports large files and file compression.
• Disadvantages: More complex than FAT.

ext4 (Fourth Extended File System)

• Description: Default file system for many Linux distributions.
• Advantages: Improved performance and reliability compared to ext3.
• Disadvantages: Not backward compatible with ext3.

12. Security Mechanisms

User Authentication

• Description: Verifies the identity of users before granting access to the system.
• Methods: Passwords, biometrics, two-factor authentication.

Access Control Lists (ACLs)

• Description: Specifies which users or system processes are granted access to objects.
• Types: Discretionary, mandatory.

Encryption

• Description: Converts data into a form that cannot be easily understood without authorization.
• Methods: Symmetric key encryption, asymmetric key encryption.

13. Real-Time Operating Systems (RTOS)

Hard Real-Time Systems

• Description: Strict deadlines must be met. Failure to meet a deadline can have catastrophic consequences.
• Applications: Aircraft control systems, medical devices.

Soft Real-Time Systems

• Description: Deadlines are important but not as strict as in hard real-time systems. Some missed deadlines may be tolerated.
• Applications: Multimedia systems, robotics.

14. Mobile Operating Systems

Android

• Description: Open-source OS developed by Google for smartphones and tablets.
• Features: Customizable user interface, wide range of apps.

iOS

• Description: Proprietary OS developed by Apple for iPhones, iPads, and iPods.
• Features: Tight integration with Apple's ecosystem, emphasis on security and privacy.

15. Server Operating Systems

Linux Server

• Description: Widely used open-source OS for servers.
• Features: Stability, security, and flexibility.

Windows Server

• Description: Operating system developed by Microsoft for servers.
• Features: Active Directory, Remote Desktop Services, PowerShell.

16. Distributed Operating Systems

Definition

• Description: Operating systems that run on multiple interconnected computers and coordinate their activities.

Characteristics

• Transparency: Hide the distribution of resources from users and applications.
• Concurrency: Allow multiple processes to run simultaneously across different machines.
• Fault Tolerance: Tolerate failures of individual machines without affecting the system as a whole.

Examples

• Google File System (GFS): Distributed file system used by Google for storing and accessing large amounts of data.
• Apache Hadoop: Framework for distributed storage and processing of large datasets.

17. Parallel Operating Systems

Definition

• Description: Operating systems designed to manage multiple processors in parallel computing environments.

Parallelism Models

• Shared Memory: Multiple processors share a common memory.
• Distributed Memory: Each processor has its own memory, and communication occurs through message passing.

Examples

• MPI (Message Passing Interface): Library for parallel programming using message passing.
• OpenMP: API for shared-memory parallel programming in C, C++, and Fortran.

18. Embedded Operating Systems

Definition

• Description: Operating systems designed for embedded systems with limited resources and specific functionality requirements.

Characteristics

• Small Footprint: Minimal memory and storage requirements.
• Real-Time Performance: Predictable and deterministic response times.
• Customization: Tailored for specific hardware and applications.

Examples

• FreeRTOS: Open-source real-time operating system kernel for microcontrollers.
• Embedded Linux: Linux distributions customized for embedded systems, such as Raspberry Pi OS.

19. Network Operating Systems

Definition

• Description: Operating systems specifically designed to support networked computing environments.

Features

• File Sharing: Allows multiple users to access and share files over a network.
• Print Sharing: Enables printers to be shared among multiple users.
• User Authentication: Controls access to network resources based on user credentials.

Examples

• Windows Server: Provides network services such as file sharing, print sharing, and user authentication.
• Linux Network Operating System (NOS): Linux distributions configured to function as network servers.

20. Virtualization

Definition

• Description: Technique of creating virtual instances of computer resources, such as hardware platforms, operating systems, storage devices, or network resources.

Types

• Hardware Virtualization: Virtualization of physical hardware resources, such as CPUs, memory, and storage.
• Software Virtualization: Virtualization of operating systems or applications within a host operating system.

Examples

• VMware vSphere: Virtualization platform for building cloud infrastructures.
• VirtualBox: Open-source virtualization software for x86 and AMD64/Intel64 computers.