Chapter 2 Operating System Structure

Operating System Structure

Chapter Overview

• Understanding the fundamentals of operating system structures is crucial for efficient program execution and resource management.

Outline

• Operating System Services

• User and Operating System Interface

• System Calls

• System Programs

• Operating System Structures

Operating System Services

• Provides execution environment for programs and services needed by users and other system programs.

• Types of Services:

  • User Interface:

    • Command-Line Interface (CLI)

    • Batch processing

    • Graphical User Interface (GUI)

  • Program Execution: Load and run programs.

  • I/O Operations: Facilitate interaction with I/O devices.

  • File-System Manipulation: Aid in reading/writing files.

  • Communications: Enable exchange of information between processes.

  • Error Detection: Detect and correct errors for reliability.

  • Resource Allocation: Distribute resources like CPU cycles to multiple jobs.

  • Accounting: Track resource usage for billing.

  • Protection and Security: Control access to system resources and protect from unauthorized access.

User and Operating System Interface

Command Line Interface (CLI)

• Allows direct command entry.

• Implemented in the kernel or via system programs.

• Examples include shells like:

  • C Shell

  • Bourne Shell

• Functions as follows:

  • Fetches user command and executes it.

  • Loads programs into memory for execution.

Batch Processing

• Manages multiple user jobs in sequence.

• Executes jobs and provides output after processing.

Graphical User Interface (GUI)

• Offers a user-friendly interface with a desktop layout.

• Uses icons to represent files and programs.

• Developed at Xerox PARC and now includes:

  • Microsoft Windows (with CLI)

  • Apple Mac OS X (Aqua interface with UNIX kernel)

  • Various UNIX/Linux distributions (CDE, KDE, GNOME).

System Calls

• Programmatic interface to OS services, often using C or C++.

• Accessed via higher-level APIs rather than direct calls.

• Common APIs include:

  • Win32 API: For Windows systems

  • POSIX API: For POSIX-compliant systems

  • Java API: For the Java Virtual Machine (JVM).

Example System Call for Copying a File

• Sequence includes:

  • Acquire input/output file names.

  • Open input file and check existence.

  • Create output file while checking for pre-existence.

  • Read from input and write to output until completion.

Types of System Calls

1. Process Control:

   • Create/terminate processes, manage memory, signal events.

2. File Manipulation:

   • Create, read, write, delete files/directories;

   • Move and copy operations.

3. Device Management:

   • Request and release device resources, perform read/write operations.

4. Information Maintenance:

   • Acquire system-related info like user number, memory status, etc.

5. Communications:

   • Manage connections, send/read messages.

6. Protection:

   • Manage user access permissions.

System Programs

• Provide an environment for program execution and development.

• Include:

  • File Manipulation Tools: For creating, renaming, listing files.

  • Status Information Tools: Retrieve system information.

  • File Modification Tools: Text editors and file search commands.

  • Programming Language Support: Compilers, assemblers, debuggers.

  • Background Services: Perform system maintenance tasks like disk checking.

  • Application Programs: Run user applications, not part of OS but interact with it.

Operating System Structures

Overview

• General-purpose OS structures vary from simple to complex designs:

  • Simple Structure: Non-modular, as seen in MS-DOS.

  • Layered Structure: Layers built on lower layers; e.g., Windows NT.

  • Microkernel Structure: Minimally sized kernel with user space for services; e.g., Minix 3.

  • Modular Structure: Loadable kernel modules, e.g., in Linux.

  • Hybrid Structure: Combines multiple models; e.g., Mac OS X, Linux.

Simple Structure

• Example: MS-DOS is a compact, non-modular system with functionality tightly integrated.

Layered Structure

• Example: Windows NT organizes the OS into layered components for modular design.

Microkernel Structure

• Example: Minix 3 emphasizes smaller kernels and message passing between components.

Modular Structure

• Adopts object-oriented principles, allowing core components to be separate and loadable as needed.

Hybrid Structure

• Combines features from various modalities for performance and security optimizations across different platforms like Linux and Mac OS X, enhancing usability.

Operating System Structures for Mobile

• iOS: Based on Mac OS X; functional adaptations for mobile hardware.

• Android: Open-source; Linux kernel foundation with its unique features, runtime environment, and application frameworks.