Operating Systems Overview and Functionality

Operating Systems Overview

• An Operating System (OS) acts as a bridge between system hardware and application software.
• Key functions of an OS include managing processes, memory, I/O resources, file systems, interrupts, and multitasking.
• Major OS families include Windows and Unix, with the Unix family comprising Linux, Mac OS X, Android, FreeBSD, Solaris, among others.

Kernel and APIs

• The core functions of an OS reside in the 'Kernel'.
• An OS provides Application Programming Interfaces (APIs) for user applications to request services from the Kernel via system calls.

User Mode vs System Mode

• The Kernel operates in a trusted 'system mode', managing CPU functions.
• User processes function in 'user mode', which has limited operational capabilities.
• The mode bit on the CPU indicates the current mode, with transitions controlled by the Kernel.
• System calls enable user processes to access kernel-level functions through traps and trap handlers.

Process Management

• A program is a static instruction set, while a process is an active instance executing those instructions.
• The OS Kernel's responsibilities include creating, terminating, and managing processes.

Process Creation and Termination

• Creating a process involves resource allocation (CPU time, memory, I/O, files) and occurs through several steps:
  • Creation of a new process object
  • Assignment of a unique process identifier (PID)
  • Allocation of memory space and resources
  • Establishment of process priority
  • Loading program code into memory
  • Initiation of execution
• Termination of a process entails:
  • Deletion of the process object
  • Release of held memory or resources

Anatomy of a Process

• A process can consist of multiple threads, with each thread having its own execution path.
• Threads share resource access like memory space and I/O within the same process, while maintaining separate stacks and register backups.
• Direct access to memory outside a process's allocated space is typically restricted.

Interrupt Management

• An interrupt signifies a device or running process requiring immediate attention.
• The processor responds by:
  • Suspending current activities
  • Saving the current system state (registers)
  • Executing an Interrupt Service Routine (ISR) to manage the event
• After ISR execution, the saved state is restored, resuming prior activities.
• Modern operating systems operate primarily through interrupts.

Multitasking

• A primary advantage of OS is enabling multitasking while coordinating shared hardware resource access.
• The OS assigns CPU access through a scheduler, which manages task execution.
• Each task's context, indicating its execution state, resides in a Task Control Block (TCB), which contains essential execution information.

This quiz covers the fundamental concepts of operating systems, including their key functions, structure, and modes of operation. It explores the roles of the kernel, user mode, and system mode interactions. Test your understanding of major OS families and their attributes.