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Questions and Answers
What is the primary objective of process scheduling?
What is the primary objective of process scheduling?
Which state does a process enter immediately after it has been initialized?
Which state does a process enter immediately after it has been initialized?
When does a process transition to the waiting/blocked state?
When does a process transition to the waiting/blocked state?
What is the role of the CPU dispatcher in process management?
What is the role of the CPU dispatcher in process management?
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What occurs during a context switch?
What occurs during a context switch?
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What is a disadvantage of the First-Come, First-Served (FCFS) scheduling algorithm?
What is a disadvantage of the First-Come, First-Served (FCFS) scheduling algorithm?
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Which scheduling algorithm is designed to minimize total processing time?
Which scheduling algorithm is designed to minimize total processing time?
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What is a defining feature of Round Robin scheduling?
What is a defining feature of Round Robin scheduling?
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What issue might arise from using the Shortest Job First (SJF) scheduling algorithm?
What issue might arise from using the Shortest Job First (SJF) scheduling algorithm?
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In Priority Scheduling, how are processes managed?
In Priority Scheduling, how are processes managed?
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Study Notes
Process Management
- Process scheduling is the mechanism by which the operating system manages the execution of processes.
- The objective is to efficiently utilize the CPU and ensure fair execution for all processes.
- Factors influencing process scheduling include:
- Resource allocation: The CPU is a finite resource, and scheduling ensures optimal utilization.
- Responsiveness: Users expect quick responses, and scheduling impacts system responsiveness.
- Throughput: Maximizing the number of processes completed per unit time.
Process States
- A process undergoes various states:
- New: This is the initial state when a process is created. The process is set up and initialized.
- Ready: After initialization, the process moves to the ready state, waiting to be assigned to a processor for execution.
- Running: The process executes on a CPU. In a multiprogramming environment, multiple processes can be in the running state simultaneously on different processors.
- Waiting/Blocked: A process enters this state when it cannot proceed until an event occurs (e.g., completing an I/O operation, acquiring a resource).
- Terminated: A process enters this state when it completes its execution; the operating system releases the associated resources.
- Suspended (Optional): Some operating systems have a suspended state, temporarily moving a process to free up resources for other processes.
CPU Dispatcher
- The CPU dispatcher is a component of the operating system responsible for making decisions about process execution on the CPU.
- Its role includes:
- Selecting the next process to run.
- Performing context switching if needed, saving and loading the context (state) of the current and new process, respectively.
- Allocating the CPU to the selected process.
CPU Scheduling Algorithms
- Several algorithms manage process selection:
- First-Come, First-Served (FCFS): Processes are executed in the order they arrive.
- Advantage: Simple and easy to understand; intuitively fair.
- Disadvantage: Potential for the "convoy effect" where short processes get stuck behind long ones.
- Shortest Job First (SJF): The shortest process is scheduled first.
- Advantage: Minimizes the total processing time.
- Disadvantage: Requires knowing the CPU burst time in advance, which is often impossible. Potential for starvation of longer processes.
- Round Robin (RR): Processes are executed for a limited time interval (time slice/quantum).
- Advantage: Fair, giving every process an equal share of the CPU.
- Disadvantage: Fairness depends on the time slice size; equal share isn't always ideal.
- Priority Scheduling: Processes are assigned priorities; the highest priority process runs next.
- Advantage: Effectively manages the relative importance of processes.
- Disadvantage: Potential for starvation if high-priority processes continuously use the CPU. Lower-priority processes might be indefinitely postponed).
- Process Aging: The Scheduler monitors processes that are not getting a chance to run and increases their priorities to ensure they eventually get scheduled.
- Multilevel Queue Scheduling: Processes are grouped into priority classes with a separate run queue for each class.
- First-Come, First-Served (FCFS): Processes are executed in the order they arrive.
Memory Management
- Memory management is the process of controlling and coordinating computer memory by assigning portions (blocks) to various processes, optimizing system performance.
- Importance: Essential for multitasking, concurrent process execution, and resource utilization.
Memory Hierarchy
- Memory is organized into a hierarchy ranging from high-speed, small-capacity registers to larger, slower main memory and storage devices.
- Different memory types include:
- Registers: Extremely fast access times but limited capacity; located directly within the CPU.
- Cache: Small-sized volatile memory, providing high-speed data access to the processor; levels (L1, L2, L3) exist. Faster than main memory but more expensive.
- Main Memory (RAM): Used for storing data and machine code currently being processed by the CPU. Volatile (contents lost when power turned off); larger capacity than cache but slower.
- Secondary Storage (Hard Drives, SSDs): Provide non-volatile storage for data and applications, even when the power is off. Much slower access times but significantly larger capacity.
Address Spaces
- Process Address Space: Each process has its own address space – the range of valid addresses a process can use, assigned and managed by the operating system.
- Kernel Address Space: The portion reserved for the operating system kernel.
Memory Allocation Strategies
- Fixed Partitioning: Memory is divided into fixed-size partitions; each process is assigned a partition. Efficient but can lead to fragmentation.
- Dynamic Partitioning: Memory divided into variable-sized partitions to accommodate different process sizes, requiring dynamic allocation algorithms.
Fragmentation
- Internal Fragmentation: Wasted memory within a partition due to allocating a larger block than necessary.
- External Fragmentation: Free memory scattered in small, non-contiguous blocks, making it challenging to allocate large contiguous blocks.
Memory Allocation Algorithms
- Various algorithms (First Fit, Best Fit, Worst Fit) manage memory allocation requests. They differ in speed, efficiency, and complexity. The choice depends on specific system needs.
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Description
Explore the essential concepts of process management in operating systems, including process scheduling and states. This quiz covers how the CPU is managed to ensure efficient execution and fair allocation of resources among processes.
