Clustered Systems vs. Multiprocessor Systems:

• Clustered Systems: Comprise multiple independent computers (nodes) connected via a network, each with its own memory and OS. They work together to perform tasks and communicate through network protocols.
• Multiprocessor Systems: Feature multiple processors sharing a common memory and OS, tightly coupled with high-speed interconnects.

Requirements for High Availability:

1. Shared Storage: Both machines must access the same data storage to maintain consistency.
2. Failover Mechanism: Automatic transfer of control to a standby machine if the primary machine fails.
3. Heartbeat Signals: Regular health checks to ensure all nodes are operational.

Method 1: Shared Disk Access

• Description: Both nodes access the same disk.
• Benefits: Simplicity, real-time data consistency.
• Disadvantages: Potential for data corruption if not managed properly, single point of failure in the disk.

Method 2: Data Replication

• Description: Each node has a copy of the data.
• Benefits: Redundancy, no single point of failure.
• Disadvantages: Complexity in maintaining data consistency, increased storage requirements.

Purpose of Interrupts:

• Function: Allow the CPU to respond to asynchronous events, improving system efficiency by handling tasks like I/O operations without continuous polling.

Interrupts vs. Traps:

• Interrupt: Generated by hardware devices to signal an event (e.g., I/O completion).
• Trap: Generated by the CPU or software to signal an error or specific condition (e.g., divide by zero).

Intentionally Generated Traps:

• Usage: Allow user programs to request services from the operating system (system calls) or handle specific conditions for debugging and error management.

HZ and Jiffies:

• HZ: Defines the number of timer interrupts per second.
• Jiffies: Counter that increments with each timer interrupt.
• Calculation: uptime (seconds) = jiffies / HZ.

CPU-DMA Coordination:

• Setup: CPU initializes DMA by setting source, destination, and transfer size in the DMA controller.

Completion Notification:

• Interrupt: DMA controller sends an interrupt to the CPU upon completing the data transfer.

Interference with User Programs:

• Cycle Stealing: DMA controller may temporarily use the CPU’s bus cycles, potentially slowing down user programs but not halting them.

Purpose of Privileged Mode:

• Function: Restricts access to critical instructions and resources, ensuring system stability and security.

Arguments for Secure OS Without Privileged Mode:

• Possible: By implementing software-based protection mechanisms like sandboxing and virtualization.

Arguments Against:

• Challenging: Less robust and efficient compared to hardware-based protection, harder to enforce strict security policies.

Multi-Level Caching:

• Reason: To balance speed and cost, with small, fast caches (L1) close to the CPU and larger, slower caches (L2/L3) shared among cores, improving overall system performance.

1. Magnetic Tapes
2. Optical Disk
3. Hard-Disk Drives
4. Nonvolatile Memory
5. Main Memory
6. Cache
7. Registers

Advantages:

• Transparency: Code is publicly available for inspection, improving security.
• Customization: Users can modify the OS to suit their needs.
• Community Support: Active user and developer communities contribute to improvements and bug fixes.

Disadvantages:

• Support: May lack professional support compared to commercial OSes.
• Compatibility: Not all software and hardware are compatible.
• Complexity: Can be difficult for non-technical users to configure and manage.

Answer: Kernel mode allows the operating system to execute privileged instructions and access hardware directly, while user mode restricts access to prevent user applications from performing potentially harmful operations. This separation helps protect the system from accidental or malicious damage.

Answer:

1. Privileged Instructions:

   • Set value of timer: Requires control over system timing mechanisms to enforce process scheduling.
   • Clear memory: Involves direct manipulation of memory, which could affect system stability.
   • Turn off interrupts: Disabling interrupts can compromise system responsiveness and stability.
   • Modify entries in device-status table: Alters the state of hardware devices, which could interfere with other processes.
   • Switch from user to kernel mode: Elevates process privileges, potentially bypassing security mechanisms.
   • Access I/O device: Direct interaction with hardware that could disrupt system operations.

2. Non-Privileged Instructions:

   • Read the clock: Only involves retrieving the current time, no modification of system state.
   • Issue a trap instruction: Used to request services from the operating system, typically allowed in user mode.

Sources:

• Silberschatz, Galvin, Gagne. Operating System Concepts (opens in a new tab)
• Javatpoint (opens in a new tab)