Jawaharlal Nehru Technological University Hyderabad MCA III OPERATING SYSTEMS Previous Question Paper (January – 2018 - R15)

System calls provide an interface between a process and the operating system. They are generally categorized into five types:

• Process Control: Manage process creation, termination, execution, and attributes (e.g., fork, exit, wait).
• File Management: Handle file operations such as create, delete, open, close, read, and write.
• Device Management: Request and release devices, read/write device status, and attach/detach devices.
• Information Maintenance: Transfer information between the user program and the OS, such as getting time, date, or system data.
• Communications: Facilitate inter-process communication (IPC) through message passing or shared memory mechanisms.

Context switching is the process of storing the state of a running process and restoring the state of another process to allow the CPU to switch tasks. The activities include:

1. Saving the current process's state (CPU registers, program counter, and stack pointer) into its Process Control Block (PCB).
2. Updating the PCB of the current process to reflect its new state (e.g., from Running to Ready or Waiting).
3. Moving the PCB to the appropriate queue (Ready or Waiting).
4. Selecting the next process to execute using the CPU scheduler.
5. Loading the saved state (registers, program counter) from the selected process's PCB into the CPU hardware.