Question Answer

Brief Notes: Operating System Services, Batch OS, and Multiprogrammed OS

(i) Operating System Services

An operating system (OS) provides a set of essential services that make the computer usable and efficient for users and applications.

• User Interface (UI): Offers a way to interact with the system, such as a command-line interface (CLI) or graphical user interface (GUI).
• Program Execution: Loads programs into memory, runs them, and handles their termination.
• I/O Operations: Manages input and output devices (keyboard, mouse, disks, printers) so applications don’t deal with hardware details.
• File System Management: Creates, reads, writes, deletes, and organizes files and directories; controls file permissions.
• Process Management: Creates and schedules processes/threads, handles synchronization and inter-process communication (IPC).
• Memory Management: Allocates and deallocates RAM, manages virtual memory, and protects one process’s memory from another.
• Communication: Enables processes to exchange data via messages, pipes, sockets, or shared memory, locally or over a network.
• Error Detection and Handling: Detects hardware and software errors and takes safe recovery actions.
• Resource Allocation: Shares CPU time, memory, and I/O devices fairly and efficiently among processes.
• Accounting and Monitoring: Tracks resource usage for performance tuning, billing (in multi-user systems), and auditing.
• Protection and Security: Enforces user authentication, access control, and safeguards against malicious or faulty programs.
• Networking Support: Provides protocols and services for data exchange across networks.

(ii) Batch Operating System

A batch operating system collects similar jobs and runs them together without user interaction during execution. Jobs are submitted in batches, often using job control commands, and processed sequentially by the system.

• Key Idea: Automate execution of large volumes of offline tasks to reduce setup and idle time.
• Workflow: Users submit jobs → system groups them → jobs are executed one after another or in batches → results are returned later.
• Typical Uses: Payroll processing, billing, report generation, data conversion.
• Advantages:
  • High throughput for repetitive, similar tasks.
  • Low CPU idle time compared to manual job loading.
  • Simpler user interaction (submit and wait for output).
• Limitations:
  • No interactive input during execution.
  • Long turnaround time for individual jobs.
  • Harder debugging and error localization.

(iii) Multiprogrammed Operating System

In a multiprogrammed operating system, multiple programs reside in main memory at the same time. When one program waits for I/O, the CPU is switched to another ready program, improving overall CPU utilization.

• Goal: Keep the CPU busy by overlapping I/O-bound and CPU-bound jobs.
• How It Works: The OS maintains several ready processes; the CPU scheduler selects one to run, and context switches occur when a process blocks or its time slice ends.
• Required Features: Memory management, protection, CPU scheduling (e.g., FCFS, SJF, Round-Robin), and job scheduling.
• Advantages:
  • Higher CPU utilization and system throughput.
  • Better resource usage compared to single-program systems.
  • Reduced average waiting time when workloads mix I/O and CPU tasks.
• Limitations:
  • Increased OS complexity and overhead (context switching, memory management).
  • Requires careful protection to prevent processes from interfering with each other.
  • Potential for starvation without fair scheduling.
• Example Scenario: While one program reads data from disk, another program uses the CPU, so the processor rarely sits idle.