Operating System Concepts

Operating System Services

• Operating systems provide services to users, process, and other systems.
• User interface: Provides a way for the user to interact with the system, using command-line, graphical user interface, or batch interfaces.
• Program execution: Operating systems load programs into memory and run them.
• I/O operations: Programs require I/O operations to interact with files or devices.
• File-system manipulation: Operating systems manage the file system, allowing users to create, delete, read, write, and manipulate files.

Operating System Structure

• There are various ways to structure an operating system.
• Simple structure, exemplified by MS-DOS, lacks modularity.
• More complex structures, like UNIX, have better separation of functions and interfaces.
• Layered approach provides abstraction, where each layer provides services to the next.
• Microkernel structure places most of the OS in user space, making the kernel smaller and more portable.

System Calls

• System calls are the interface for programs to access the operating system services.
• They are typically written in high-level languages like C or C++.
• Applications generally interact with system calls through Application Programming Interfaces (APIs), such as Win32 API, POSIX API, and Java API.

Types of System Calls

• Process Control: creation, termination, waiting, and manipulating processes.
• File Management: creation, deletion, opening, closing, reading, and writing files.
• Device Management: requesting, releasing, reading, writing, and managing devices.
• Information Maintenance: retrieving system information like time, date, and system data.
• Communications: establishing connections between processes, sending and receiving messages, and managing shared memory.
• Protection: controlling access to resources and managing permissions.

System Programs

• System programs provide a user-friendly environment for development and execution.
• Examples include file manipulation tools, status information displays, programming language support, program loading and execution tools, communication tools, background services, and application programs.
• They offer a higher-level interface to the system services compared to system calls.

Operating System Design and Implementation

• Operating system design involves defining goals, specifications, and principles.
• User goals: convenience, ease of use, reliability, safety, and speed.
• System goals: ease of design and implementation, flexibility, reliability, absence of errors, and efficiency.
• Separation of policy from mechanism: Policies specify what to do, while mechanisms define how to do it, allowing for flexibility and adaptability.
• Implementation involves using a variety of programming languages, including assembly, C, C++, scripting languages, and other specialized tools. ### iOS
• Developed by Apple
• Cocoa Touch Objective-C API for developing apps
• Media services layer for graphics, audio, and video
• Core services provide cloud computing and databases
• Core operating system based on Mac OS X kernel

Android

• Developed by Open Handset Alliance, mostly Google
• Open source
• Similar stack to iOS
• Based on the Linux kernel but modified
• Provides process, memory, and device driver management
• Adds power management
• Runtime environment includes a core set of libraries and the Dalvik virtual machine
• Apps developed in Java plus Android API
  • Java class files compiled to Java bytecode then translated to executables that run in the Dalvik VM
•  Libraries include frameworks for a web browser (webkit), database (SQLite), multimedia, and a smaller libc

Android Architecture

• Uses a layered architecture
• Provides a Linux kernel and a set of system services
• Applications run in a user space above the system services

Operating System Debugging

• Finding and fixing errors or bugs
• Operating systems generate log files containing error information
• Failure of an application can generate a core dump file (captures memory of the process)
• Operating system failure can generate a crash dump file (containing kernel memory)
• Beyond crashes, performance tuning can optimize the system performance
  • Sometimes using trace listings of activities, recorded for analysis
  • Profiling is periodic sampling of the instruction pointer looking for statistical trends
• Kernighan’s Law: "Debugging is twice as hard as writing the code in the first place. Therefore, if you write the code as cleverly as possible, you are, by definition, not smart enough to debug it."

Explore key concepts and services provided by operating systems, including user interfaces, program execution, and file-system manipulation. Understand different structures of operating systems and their functionalities, from simple designs to complex layered approaches.