A1.3.5 Role of the Operating System in Managing Multitasking and Resource Allocation (HL only) Notes

Understanding Multitasking and Resource Allocation

The Challenges of Multitasking

1. Task Scheduling: Deciding which process gets CPU time and when.
2. Resource Contention: Multiple processes competing for the same resource.
3. Deadlock: A situation where processes are stuck waiting for resources held by each other.

Resource Allocation Mechanisms

1. Memory Management
   1. Paging
      1. Physical memory is divided into fixed-size blocks called pages.
      2. Each process has a virtual address space mapped to these physical pages.
      3. Gives the illusion of a large, continuous memory space.
      4. Improves efficiency in memory usage.
   2. Segmentation
      1. Memory is divided into variable-sized segments (e.g. code segment, data segment).
      2. Each process has its own logical segments.
      3. Allows for logical organisation and improved memory protection.
   3. Virtual Memory
      1. Combines paging and segmentation.
      2. Extends RAM by using secondary storage (e.g. HDD or SSD).
      3. Allows processes to access more memory than physically available.
2. Device Management
   1. The operating system uses device drivers to communicate with specific hardware components.
   2. Device drivers provide a consistent method of accessing peripherals (e.g. printers, network cards).
   3. Device management prevents resource conflicts between processes.
3. File Systems
   1. The file system is an abstraction layer that organises data on storage hardware into files and folders.
   2. Common file systems: include NTFS (Windows), APFS (macOS), and ext4 (Linux).
   3. Data is stored in fixed-size blocks, typically several kilobytes in size.
   4. The OS translates file operations (read/write) into block-level operations on the disk.
4. Resource Monitoring and Limits
   1. The OS tracks how processes use system resources such as CPU, memory, and disk I/O.
   2. Limits and quotas can be applied to prevent any single process from overusing resources.
   3. These controls help maintain system stability and fairness across processes.

Task Scheduling: Balancing Fairness and Efficiency

1. Fairness: Ensuring all processes get a chance to execute.
2. Efficiency: Maximizing CPU utilization and minimizing wait times.

Resource Contention: Managing Competition

1. CPU: Scheduling algorithms allocate CPU time.
2. Memory: Virtual memory and paging ensure efficient use.
3. I/O Devices: Device drivers manage access to peripherals.

Deadlock: Preventing System Standstills

1. Detection: Identifying deadlocks when they occur.
2. Prevention: Using algorithms to avoid circular dependencies.
3. Resolution: Terminating or rolling back processes to free resources.

The Role of the OS in Resource Allocation

1. Memory Management:
   1. Paging: Divides memory into fixed-size blocks.
   2. Segmentation: Organizes memory into logical segments.
   3. Virtual Memory: Extends physical memory using disk space.
2. CPU Scheduling:
   1. Pre-emption: Interrupting a process to allow a higher-priority task to run.
   2. Context Switching: Saving and restoring process states during multitasking.
3. Device Management:
   1. Device Drivers: Interface between the OS and hardware.
   2. I/O Scheduling: Prioritizes access to peripherals.

Strategies for Effective Multitasking

1. Scheduling Algorithms:
   1. Round Robin: Ensures fairness by giving each process a fixed time slice.
   2. Priority Scheduling: Allocates CPU time based on process importance.
2. Resource Monitoring:
   1. The OS tracks resource usage and enforces limits to prevent any process from monopolizing resources.
3. Deadlock Prevention:
   1. Algorithms like deadlock avoidance and detection ensure system stability.

The Significance of Multitasking and Resource Allocation

1. System Performance: Efficient multitasking ensures smooth operation even under heavy loads.
2. User Experience: Users can run multiple applications without noticeable delays.
3. System Stability: Preventing deadlocks and resource contention maintains system reliability.