Podcast
Questions and Answers
Which operating system was the first to introduce time-sharing?
Which operating system was the first to introduce time-sharing?
What is a key feature of Shortest Job First (SJF) scheduling?
What is a key feature of Shortest Job First (SJF) scheduling?
Which of the following is NOT a condition for deadlock to occur?
Which of the following is NOT a condition for deadlock to occur?
In the context of deadlock, what does 'No Preemption' mean?
In the context of deadlock, what does 'No Preemption' mean?
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What is the primary role of an operating system?
What is the primary role of an operating system?
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Which scheduling algorithm can lead to starvation of lower-priority processes?
Which scheduling algorithm can lead to starvation of lower-priority processes?
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Which cache level is the smallest, closest, and fastest?
Which cache level is the smallest, closest, and fastest?
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What does Fair Share Scheduling ensure?
What does Fair Share Scheduling ensure?
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What type of cache miss occurs when data is accessed for the first time?
What type of cache miss occurs when data is accessed for the first time?
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Which cache replacement policy writes data to memory after it has been cached?
Which cache replacement policy writes data to memory after it has been cached?
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What does the completion time of a process refer to?
What does the completion time of a process refer to?
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In a directed acyclic graph (DAG), what is its primary characteristic?
In a directed acyclic graph (DAG), what is its primary characteristic?
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Which of the following best describes a conflict miss in cache memory?
Which of the following best describes a conflict miss in cache memory?
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What is the purpose of a resource allocation graph (RAG)?
What is the purpose of a resource allocation graph (RAG)?
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Which metric indicates the total amount of active time the CPU spends processing tasks?
Which metric indicates the total amount of active time the CPU spends processing tasks?
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Which data structure allows multiple edges between the same pair of vertices?
Which data structure allows multiple edges between the same pair of vertices?
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What is the purpose of a semaphore in process synchronization?
What is the purpose of a semaphore in process synchronization?
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Which of the following best defines the Critical Section Problem?
Which of the following best defines the Critical Section Problem?
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In the context of memory management, which type of fragmentation refers to gaps between allocated blocks?
In the context of memory management, which type of fragmentation refers to gaps between allocated blocks?
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What characterizes preemptive scheduling in operating systems?
What characterizes preemptive scheduling in operating systems?
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Which synchronization mechanism ensures that multiple readers can access data while writers have exclusive access?
Which synchronization mechanism ensures that multiple readers can access data while writers have exclusive access?
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Study Notes
OS History and Overview
- Operating systems (OS) manage computer hardware and software resources.
- ENIAC was an early computer developed in the 1940s.
- GM-NAA I/O was the first OS for the IBM 709 in the 1950s.
- CTSS, developed at MIT in the 1960s, was the first time-sharing OS.
- Unix emerged in the 1970s, introducing multitasking and multi-user capabilities.
- Windows, released in the 1980s, provided a GUI-based OS for general users.
- Linux, launched in the 1990s, is an open-source OS popular in servers and embedded systems.
- Android and iOS, both released in the 2000s, dominate the mobile operating system market.
Scheduling Algorithms
- First-Come, First-Served (FCFS) executes processes in the order they arrive.
- Shortest Job First (SJF) prioritizes processes with the shortest burst time.
- Round Robin (RR) allocates a fixed time quantum for each process.
- Priority Scheduling can lead to starvation of lower-priority processes.
- Multilevel Feedback Queue uses multiple queues to balance long and short processes.
- Real-Time Scheduling techniques include Rate-Monotonic and Earliest Deadline First (EDF).
- Fair Share Scheduling distributes resources equally among user groups.
- Priority Inversion occurs when a lower-priority process holds a resource for a higher-priority one; resolved by Priority Inheritance.
Deadlock
- Deadlock occurs when processes wait indefinitely for resources held by each other.
- Coffman Conditions for deadlock include:
- Mutual Exclusion: At least one resource is held non-sharably.
- Hold and Wait: A process waits for additional resources while holding some.
- No Preemption: Resources cannot be forcibly removed from a process.
- Circular Wait: Processes form a chain waiting on each other.
- Deadlock detection involves checking for cycles in a Resource Allocation Graph (RAG).
- Recovery methods include aborting processes or preempting resources.
- Preventing deadlocks can be computationally expensive.
Cache
- Purpose of cache: Reduce access time to frequently used data.
- Cache levels:
- L1: Smallest, closest, fastest.
- L2: Larger, slower than L1.
- L3: Shared among CPU cores, largest, and slowest.
- Cache Associativity types include Direct-Mapped, Fully Associative, and Set-Associative.
- Cache miss types:
- Compulsory Miss: Data accessed for the first time.
- Capacity Miss: Cache cannot accommodate all data.
- Conflict Miss: Eviction occurs due to associativity rules.
- Replacement policies: Least Recently Used (LRU), First-In First-Out (FIFO), and Least Frequently Used (LFU).
- Cache coherence in multi-core systems is maintained using protocols like MSEI.
- Write policies: Write-Back (caches first, writes later) vs. Write-Through (caches and writes simultaneously).
Time Concepts in Scheduling
- Arrival Time: Moment a process enters the ready queue.
- Burst Time: Total CPU time needed for process execution.
- Completion Time: When a process finishes execution.
- Turnaround Time: Total time from arrival to completion.
- Waiting Time: Duration spent in the ready queue.
- Response Time: Time until the first response is received.
- CPU Utilization: Percentage of CPU active time.
- Throughput: Count of processes completed per time unit.
- Context Switch: Overhead from switching between processes.
Graphs (Vertices and Edges)
- Vertices (nodes) represent entities or points in a graph, like processes or resources.
- Edges (arcs) are connections between vertices, signifying relationships.
- Edges can be directed (one-way) or undirected (two-way) and may have weights.
- Resource Allocation Graph (RAG) is used for deadlock detection, showing processes and resources.
- Cycles in RAG indicate potential deadlocks.
- Weighted Directed Graphs apply costs in shortest path calculations, such as Dijkstra's Algorithm.
- Directed Acyclic Graph (DAG) is used for scheduling tasks; it has no cycles.
- Depth-First Search (DFS) detects cycles in graphs.
- Topological Sorting determines the order of tasks in a DAG.
- Multigraphs allow multiple edges between the same vertices.
Process Synchronization
- Race Condition occurs when shared data is accessed unsynchronized, leading to unpredictable outcomes.
- Semaphore: A counter controlling access to shared resources.
- Monitors encapsulate shared resources for high-level synchronization.
- Critical Section Problem ensures mutual exclusion in shared access.
- Readers-Writers Problem allows multiple readers but mandates exclusive access for writers.
- Spinlocks: Processes wait while spinning for a lock, inefficient for long waits.
- Barriers synchronize processes to ensure they reach specific milestones concurrently.
- Process synchronization prevents data corruption by controlling process execution order using semaphores and locks.
Memory Management
- Paging divides memory into fixed blocks, mitigating fragmentation.
- Segmentation organizes memory into logical segments (e.g., functions, arrays).
- Virtual Memory uses disk space to create an illusion of larger memory.
- Memory Protection ensures one process cannot access another's memory.
- Fragmentation types include:
- Internal Fragmentation: Wasted space within allocated memory blocks.
- External Fragmentation: Unused gaps between allocated memory sections.
Additional Concepts
- Preemptive Scheduling allows the CPU to be taken from processes before completion.
- Non-Preemptive Scheduling means a process holds the CPU until it finishes.
- Throughput quantifies total process completions in a specified timeframe.
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Description
This quiz covers the history and evolution of operating systems from the 1940s to the present. Learn about key developments, including ENIAC, Unix, Windows, and modern mobile operating systems like Android and iOS. Test your knowledge on how these systems have transformed computing.
