Fundamentals of Operating Systems

Introduction

• Definition and Importance:
  • Provides abstraction and arbitration.
  • Abstraction hides hardware details; arbitration manages access to shared resources.
• Key Components Managed:
  • CPU, memory hierarchy, input/output devices, power, and system management.
  • Involved in energy conservation.

Abstraction

• Definition: Hiding hardware differences to provide a uniform interface for applications.
• Example from the 1990s: Games required specific configurations for video and sound cards.
• Abstraction's Advantage: Allows hardware variety without needing separate software for each device.
• Modern Example: Switching between Intel and AMD processors without needing separate applications.

Arbitration

• Definition: Managing access to shared hardware so multiple applications can run concurrently without interference.
• Examples:
  • Switching between applications (CPU management).
  • Memory allocation.
  • Isolating applications to prevent system crashes.

Applications of Abstraction and Arbitration

• Support for multiple CPUs and intelligent resource management.
• Enabling applications to use different hardware devices (e.g., webcams, hard disks) without unique code for each.

System Layers

• Layer Cake Model:
  • Bottom: Hardware
  • Middle: Operating System (OS)
  • Top: Applications and Libraries
• Kernel: Core part of the OS, everything outside is user space.
• OS Functions: Managing access and sharing hardware resources (system calls and interrupts).

Types of Operating Systems

• Microsoft Windows:
  • Pre-installed on PCs, most popular desktop OS.
  • Being surpassed by tablets running Unix-like systems.
• Unix-like Systems:
  • Includes BSD, Mac OS X, Linux (and Android).
  • Multi-user, based on Multics (1969) by Bell Labs.
• Real-time, mainframe, embedded OS examples.

Memory Hierarchy in Systems

• Components:
  • CPU registers, cache, random access memory (RAM), persistent storage (disks, SSDs).
• Form Factors:
  • ATX, microATX, miniATX for desktops and workstations, rack-mounted servers for data centers.

Persistent Storage

• Hard Disk Drives (HDDs): Mechanical, magnetic storage, subject to seek time and rotational delay.
• Solid State Drives (SSDs): Faster, use flash memory, limited write cycles (wear leveling management).

Backups

• Importance of backing up data to prevent loss.
• Types of Backup Media:
  • Optical Disks (CDs, DVDs, Blu-ray), Flash Drives, Tape Drives, Cloud Storage.

Disk Scheduling

• Purpose: Managing disk I/O to improve performance.
• Classical Algorithms: First-come-first-serve, elevator algorithms (scan, look, C-scan, C-look), shortest seek time first (obsolete with modern drives).
• Modern Considerations: Native Command Queuing (NCQ) for internal disk scheduling.

Software Development Cycles

• Steps: Planning, requirements analysis, design, coding, testing, deployment, maintenance.
• Development Models: Code-and-Fix, Waterfall, Iterative-Incremental (Agile, Rapid Application Development, Extreme Programming).
• Formal Methods: Required for life/safety-critical systems (e.g., cleanroom engineering).

File Systems

• Purpose: Laying out data on persistent storage, storing metadata, ensuring reliable data retrieval.
• Issues: Fragmentation (internal, external), Journaling.
• Layouts: File Allocation Table (FAT), inodes, extents.

Requirements Analysis

• Types of Projects: Greenfield vs. Re-engineering.
• Key Roles: Stakeholders, interests, primary and supporting actors.
• Requirements Types: Functional (what the system does), Non-functional (quality attributes, what the system is).

CPU and Multi-Programming

• Multi-programming: Running multiple processes concurrently by CPU switching.
• Hardware Requirements: Interrupts, CPU protection levels (kernel/user mode), mode switches.

Kernel Architectures

• Functions of the Kernel: Abstraction, arbitration, ensuring system stability and performance.
• Types: Monolithic (e.g., Linux, Windows NT), Microkernels (e.g., L4, Mach).
• Hybrid Designs: Combine features of both for performance and modularity.

Unified Modeling Language (UML)

• Purpose: Standardized way to model software designs (classes, behaviors, interactions).
• Types of Diagrams: Structural (class diagrams), Behavioral (activity, state machine), Interaction.

Memory Allocation

• Dynamic: Allocating memory as needed to prevent space wastage and handle high multiprogramming.
• Methods: Power of two, buddy system, slab allocation (for kernels).

Process Management

• Process Contexts: Information needed to stop and restart a process (CPU registers, program counter, memory contents).
• States: New, ready, running, waiting, terminated.
• Scheduling: Job (long-term), Midterm, and Short-term (CPU) scheduling.
• Process Control Blocks (PCBs): Arrays and linked lists managing processes' state information.

Conclusion and Key Takeaways

• Operating systems are essential for managing hardware resources and providing a uniform interface for applications.
• Abstraction and arbitration are fundamental to managing the diverse and concurrent needs of applications and hardware.
• Comprehensive understanding of OS functions, different kernel types, and effective memory and process management techniques is crucial for designing and maintaining robust, efficient computer systems.