Podcast
Questions and Answers
What does the Readers-Writers Problem ensure when multiple processes access shared data?
What does the Readers-Writers Problem ensure when multiple processes access shared data?
What is the main purpose of process synchronization?
What is the main purpose of process synchronization?
What does paging in memory management aim to avoid?
What does paging in memory management aim to avoid?
Which type of scheduling allows a process to retain the CPU until it finishes execution?
Which type of scheduling allows a process to retain the CPU until it finishes execution?
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What is external fragmentation in memory management?
What is external fragmentation in memory management?
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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 evicts the least recently used data?
Which cache replacement policy evicts the least recently used data?
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In a write-back cache, when is the data written to the main memory?
In a write-back cache, when is the data written to the main memory?
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Which operating system introduced multitasking and multi-user capabilities?
Which operating system introduced multitasking and multi-user capabilities?
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What does turnaround time represent in process scheduling?
What does turnaround time represent in process scheduling?
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What is the main condition that must hold true for a deadlock to occur?
What is the main condition that must hold true for a deadlock to occur?
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What does a cycle in a Resource Allocation Graph (RAG) indicate?
What does a cycle in a Resource Allocation Graph (RAG) indicate?
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Which graph algorithm is commonly used to detect cycles in directed graphs?
Which graph algorithm is commonly used to detect cycles in directed graphs?
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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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What is a semaphore used for in process synchronization?
What is a semaphore used for in process synchronization?
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Which cache level is the largest and shared among CPU cores?
Which cache level is the largest and shared among CPU cores?
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What defines the First-Come, First-Served (FCFS) scheduling algorithm?
What defines the First-Come, First-Served (FCFS) scheduling algorithm?
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What characterizes a Directed Acyclic Graph (DAG)?
What characterizes a Directed Acyclic Graph (DAG)?
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Which condition does NOT contribute to deadlock formation?
Which condition does NOT contribute to deadlock formation?
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Which recovery method for deadlock involves reallocating resources from some processes?
Which recovery method for deadlock involves reallocating resources from some processes?
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What is a characteristic of real-time scheduling algorithms?
What is a characteristic of real-time scheduling algorithms?
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Study Notes
OS History and Overview
- Operating Systems manage computer hardware and software resources.
- ENIAC was one of the first electronic computers developed in the 1940s.
- GM-NAA I/O was an early OS created for the IBM 709 in the 1950s.
- CTSS, developed at MIT in the 1960s, was the first time-sharing operating system.
- Unix, launched in the 1970s, introduced multitasking and multi-user capabilities, forming the basis for modern OS.
- Windows emerged in the 1980s as a graphical user interface OS targeted at general users.
- Linux, introduced in the 1990s, is an open-source OS popular in servers and embedded systems.
- Android and iOS became the dominant mobile operating systems in the 2000s.
Scheduling Algorithms
- First-Come, First-Served (FCFS) processes execute in the order of arrival.
- Shortest Job First (SJF) prioritizes processes with the shortest burst time.
- Round Robin (RR) allocates a fixed time quantum to each process in rotation.
- Priority Scheduling can lead to starvation, where lower-priority processes wait indefinitely.
- Multilevel Feedback Queue organizes multiple queues based on priority levels and burst characteristics.
- Real-Time Scheduling involves Rate-Monotonic and Earliest Deadline First (EDF) methods for time-sensitive tasks.
- Fair Share Scheduling allocates resources equally among user groups.
- Priority Inversion occurs when a lower-priority process blocks a higher-priority one, resolved through Priority Inheritance.
Deadlock
- Deadlock refers to a state where processes wait indefinitely for resources held by one another.
- Coffman Conditions outline four necessary criteria for deadlocks:
- Mutual Exclusion: Resource held in a non-sharable mode.
- Hold and Wait: Processes holding resources are waiting for additional resources.
- No Preemption: Resources cannot be taken forcibly from processes.
- Circular Wait: A circular chain of processes waiting on each other.
- Deadlock detection involves checking for cycles in a Resource Allocation Graph (RAG).
- Recovery methods include aborting processes or resource preemption to reallocate resources.
- Deadlock prevention can be computationally intensive.
Cache
- Caching reduces the time needed to access frequently used data.
- Cache levels vary by speed and size:
- L1 is the fastest but smallest.
- L2 is larger and slower than L1.
- L3 is shared among CPU cores and the largest but slowest.
- Cache associativity types include:
- Direct-Mapped,
- Fully Associative,
- Set-Associative.
- Cache misses occur in three forms:
- Compulsory Miss: First-time data access.
- Capacity Miss: Cache lacks space for all needed data.
- Conflict Miss: Data evicted due to associativity rules.
- Least Recently Used (LRU) is a common policy for cache replacement.
- Cache coherence in multi-core systems employs protocols like MSEI.
- Write-Back caches write data to cache first and to memory later, whereas Write-Through ensures simultaneous writing to both.
Time Concepts in Scheduling
- Arrival Time: When a process is added to the ready queue.
- Burst Time: Total CPU time required for a single process.
- Completion Time: When a process execution finishes.
- Turnaround Time: The total time from arrival to completion.
- Waiting Time: Time a process waits in the ready queue.
- Response Time: Time taken from arrival until the first response, particularly important for interactive systems.
- CPU Utilization: Percentage of time the CPU is actively processing tasks.
- Throughput: Number of processes completed within a specified time frame.
- Context Switch: Overhead incurred when switching between processes.
Graphs (Vertices and Edges)
- Vertices represent entities such as processes, resources, or data points.
- Edges are connections between vertices, indicating relationships or interactions; they may be directed or undirected, sometimes weighted.
- A Resource Allocation Graph (RAG) assists in detecting deadlocks, with cycles indicating potential deadlocks.
- Weighted Directed Graphs utilize edge weights for algorithms like Dijkstra's for shortest paths.
- Directed Acyclic Graphs (DAG) are employed for scheduling tasks without cycles.
- Depth-First Search (DFS) is useful for cycle detection in graphs.
- Topological Sorting in a DAG helps determine task execution order.
- Multigraphs allow for multiple edges connecting the same pair of vertices.
Process Synchronization
- Race Condition: Unpredictable outcomes from unsynchronized access to shared data.
- Semaphore: A synchronization tool that regulates access to shared resources through a counter.
- Monitors: High-level constructs providing synchronized access to resources.
- Critical Section Problem: Ensures exclusive access for one process in critical sections.
- Readers-Writers Problem: Allows multiple readers access but grants exclusive access to writers.
- Spinlocks allow a process to wait (or spin) while trying to acquire a lock.
- Barriers ensure that all processes reach a sync point before continuing.
- Effective process synchronization prevents conflicts and data corruption.
Memory Management
- Paging divides memory into equal-sized blocks, reducing fragmentation issues.
- Segmentation organizes memory into logical units like functions or arrays.
- Virtual Memory employs disk space to extend perceived memory capacity.
- Memory Protection restricts access among processes, safeguarding data integrity.
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Fragmentation types include:
- Internal Fragmentation: Wasted space within allocated blocks.
- External Fragmentation: Unallocated gaps between allocated blocks post-deallocation.
Additional Concepts
- Preemptive Scheduling allows the CPU to interrupt processes before completion.
- Non-Preemptive Scheduling mandates that processes keep the CPU until they finish.
- Throughput measures the number of processes finalized in a set timeframe.
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Description
Explore the evolution of operating systems from the early ENIAC and GM-NAA I/O systems to the contemporary giants like Android and iOS. This quiz covers key milestones in OS development, including significant innovations like Unix's multitasking capabilities and the rise of open-source software with Linux. Test your knowledge on how these systems manage computer hardware and software.
