Operating Systems Structures and Processes

Question 1

What are the key services provided by an OS?

Answer 1

• UI: CLI, GUI
• Program Execution: Loads and runs programs
• I/O Operations: Manages devices
• File-System Manipulation: Creates/deletes files, enforces permissions
• Communication: Shared memory or message passing between processes
• Error Detection: Handles hardware/software errors
• Resource Allocation: Manages CPU, memory
• Accounting & Security: Tracks usage and enforces access control

Question 2

What is a system call?

Answer 2

A programming interface to request OS services (e.g. open(), fork())

Question 3

How are parameters passed to system calls?

Answer 3

Via registers, memory blocks or the stack

Question 4

Compare Windows and Unix system calls

Answer 4

• Windows: CreateProcess(), ReadFile()
• Unix: fork(), read()

Question 5

What are the parts of a process?

Answer 5

• Text: Code + program counter
• Stack: Temporary data
• Data: Global variables
• Heap: Dynamically allocated memory

Question 6

What are the process states?

Answer 6

• New: Created
• Ready: Waiting for CPU
• Running: Executing
• Waiting: Blocked
• Terminated: Finished

Question 7

What is stored in a PCB?

Answer 7

Process state, PC, registers, scheduling info, memory limits, I/O status

Question 8

What are the key queues in process scheduling?

Answer 8

• Job Queue: All processes
• Ready Queue: Processes in memory ready to execute
• Device Queue: Processes waiting for I/O

Question 9

Compare short-term and long-term schedulers

Answer 9

• Short-term: Selects next process for CPU (frequent, fast)
• Long-term: Controls multiprogramming by loading processes into memory (infrequent, slow)

Question 10

Process Lifecycle example

Answer 10

1. Ready -> Running: Dispatched by short-term scheduler
2. Running -> Waiting: I/O request or event wait
3. Waiting -> Ready: I/O completion
4. Running -> Terminated: Process exits