Operating Systems

1. What is OS? What are its important functions?

• An Operating System (OS) is software that manages computer hardware and software resources
• Functions:
  • Process management: Allocates CPU time (e.g., when you run Chrome and Word simultaneously)
  • Memory management: Allocates and tracks RAM (e.g., closing unused apps frees memory)
  • File system management: Organizes data storage (e.g., saving files to specific folders)
  • Device management: Controls hardware (e.g., printing documents)
  • Security: Manages user permissions (e.g., admin vs. standard user rights)
  • User interface: Provides ways to interact (e.g., Windows GUI or command line)

2. What is system call? How it is executed?

• System calls are interfaces between user programs and OS kernel services
• Execution process:
  • Application makes system call request (e.g., open() to access a file)
  • Parameters placed in registers/stack
  • Control transfers to kernel mode via interrupt
  • Kernel validates and executes request
  • Results returned to application
  • Example: When you open a file in an app, the open() system call requests file access from kernel

3. Explain terms: Multi-programming, Multi-tasking, Multi-threading, Multi-processing and Multi-user?

• Multi-programming: Multiple programs loaded in memory, CPU switches between them
  • Example: Having Word, Excel, browser in memory simultaneously
• Multi-tasking: Multiple tasks execute concurrently by time-sharing
  • Example: Playing music while writing a document
• Multi-threading: Single process contains multiple execution flows
  • Example: Web browser rendering page while downloading files
• Multi-processing: Multiple CPUs/cores work simultaneously
  • Example: Video rendering using all CPU cores
• Multi-user: Multiple users access system resources simultaneously
  • Example: University computer lab where many students log in to the same system

4. Explain process life cycle.

• Creation: Process is created (e.g., clicking an app icon)
• Ready: Process waiting for CPU time
• Running: Process executing on CPU (e.g., app responding to input)
• Waiting/Blocked: Process waiting for resource/event (e.g., waiting for file download)
• Terminated: Process execution complete (e.g., closing an application)
• Real-life example: When opening Microsoft Word, it's created, moves to ready, runs when given CPU time, waits when saving files, terminates when closed