Question

The following four requests could come in to an operating system as it is running on a computer system: \- The clock in the computer has just "ticked," and we need to update a seconds counter. \- The program running on processor 2 is trying to perform an illegal operation code. \- Someone pulled the plug on the power supply, and the system will run out of power in \(50 \mathrm{msec}\). \- The disk has just read the character that passed under the read/write head, and it wants to store it in memory before the next one arrives. In what order should the operating system handle these requests?

Short answer

Handle requests in this order: power supply issue, illegal operation code, disk I/O, clock tick update.

Step-by-step solution

Identify Priority of Each Request

In computer systems, there are different priority levels for how requests should be handled by the operating system. The key priority levels are often: 1. Power failure and recovery 2. Hardware failure or significant problems (e.g., illegal operation code) 3. Common timeouts and operative functions (e.g., clock tick) 4. I/O operations that are time-sensitive, but generally lower priority than emergencies. For this task: - A power supply failure (request 3) should take the highest priority as it is critical. - An illegal operation code on processor 2 (request 2) is also crucial as it could indicate a severe failure or security issue. - Updating the seconds counter (request 1) is a regular function that doesn't demand immediate attention. - A disk I/O request (request 4) needs to be performed in a timely manner, but is normally handled after more critical system-level tasks.

Rank the Requests by Priority

Based on the priorities identified in Step 1, rank the requests from highest to lowest priority: 1. Power supply failure (request 3): This is a critical emergency since the system will shut down imminently without intervention. 2. Illegal operation code (request 2): This could prevent system stability or indicate a vulnerability. 3. Disk I/O operation (request 4): While not as urgent as the first two, it needs timely processing to avoid losing data. 4. Clock tick update (request 1): Regular processing task with the least immediate urgency.

Determine the Order of Execution

Based on the ranking from Step 2, order the requests to determine how the operating system should execute them: 1. Handle the power supply issue immediately to ensure system integrity and prevent data loss or corruption. 2. Address the illegal operation code right after, because it can significantly affect the system's functioning. 3. Perform the disk I/O since it involves non-urgent data processing but still requires timely handling. 4. Finally, update the seconds counter, as it's the least urgent.

Key concepts

Request Prioritization

Prioritizing requests is crucial for an operating system to function effectively. Different tasks require varying levels of urgency. For instance, critical events such as power failures need to be handled first to avoid shutting down the system. Next, tasks that might indicate potential system instability, like illegal operation codes, are addressed. After that, important but less urgent tasks like input/output (I/O) operations can be dealt with. Lastly, routine updates, such as clock ticks, can be prioritized lower. This hierarchy ensures that the most pressing issues receive immediate attention, maintaining the system's overall safety and functionality.

System Stability

System stability is vital to ensure that an operating system runs smoothly without crashes or vulnerabilities. Events like illegal operation codes pose significant risks. If not addressed quickly, they can lead to malfunctions or security breaches. Stabilizing the system means efficiently managing and resolving these issues to keep the system operational.
It's like preventing the building blocks of a tower from collapsing—each decision impacts the overall integrity. The operating system must balance resolving these critical issues while still handling less severe tasks. Ensuring stability provides a reliable user experience and prolongs the lifespan of the hardware and software.

I/O Operations

I/O operations, or input/output operations, involve data exchange between the system's hardware and the external environment. They can include reading a character from a disk or writing data to storage. These operations require timely execution but usually come after more essential system-level tasks.

• Disk reads and writes are part of I/O operations, crucial for data integrity.
• While important, they are often deprioritized in emergencies.

Properly managing I/O operations ensures that the system can interact with peripheral devices efficiently and reliably, impacting overall performance.

Hardware Failure

Hardware failures are critical incidents that necessitate immediate attention. A loss of power supply, for example, poses a direct threat to system functionality. It can halt all operations and result in significant data loss. Such failures need immediate rectification to maintain system integrity.
The operating system must constantly monitor hardware health and prepare for potential failures. Unlike software issues, hardware problems often have irreversible consequences. As such, prioritizing hardware failures is essential to safeguard the system against unexpected shutdowns and data corruption.

Time Management

Time management is about how an operating system schedules and executes various tasks efficiently. It's a balancing act involving urgency and resource allocation. For instance, updating a clock tick is a low-priority task compared to addressing an imminent power failure.

• Tasks are queued based on urgency.
• Efficient time management prevents bottlenecks and ensures a smooth workflow.

The operating system must allocate time and resources wisely to ensure that all tasks receive attention. This effective management enhances performance and reliability, allowing the system to function optimally even under stress.