Operating Systems Exam Study Notes

An operating system is a software that manages hardware and software resources, providing a platform for other programs to run. It acts as an intermediary between the user and the computer's hardware.

Schedulers are programs responsible for selecting the next process to execute and allocating CPU time to them. They determine the order in which processes will run on the CPU.

Memory management is crucial because it ensures efficient use of limited RAM by allocating and deallocating memory space to processes as needed, preventing memory conflicts and crashes.

Disk scheduling aims to optimize the order in which disk I/O requests are handled, minimizing seek time (the time spent moving the read/write head) and improving overall disk performance.

Deadlocks occur when two or more processes are stuck in a waiting loop, each holding a resource that the other needs, preventing both from progressing.

Rotational latency is the time it takes for the desired sector to rotate under the read/write head of the disk. It represents the delay due to the mechanical rotation of the disk platter.

A scheduling queue is a data structure used to hold processes waiting to be scheduled and executed by the CPU. It acts as a waiting list for processes.

Time-sharing allows multiple processes to share the CPU, giving each process a short burst of time before switching to another. This creates the illusion that all processes are running simultaneously, improving system utilization and responsiveness.

Process states represent the different stages a process can go through during its lifetime. Common states include: New, Ready, Running, Waiting, and Terminated.

Swapping is a memory management technique that moves processes between main memory (RAM) and secondary storage (disk) to free up space for other processes or manage limited RAM resources. It can improve system responsiveness, but it comes with the overhead of disk I/O.

File access methods refer to the ways in which data is accessed or retrieved from a file. Common methods include sequential access, direct access, and indexed sequential access.

Mutual exclusion is a necessary condition for deadlock to occur. When two or more processes need exclusive access to the same resource, this can contribute to a deadlock if both processes are waiting for each other to release the resource.

Threads are lightweight processes that share the same address space and resources. They execute concurrently within a single process, allowing for efficient resource utilization and improved performance.

A distributed operating system (DOS) is a system where multiple computers (nodes) are interconnected and act as a single system, sharing resources and communicating with each other. It allows for increased performance, scalability, and resilience.

FCFS (First Come, First Served) is a non-preemptive scheduling algorithm where processes are served in the order they arrive. Simple to implement, but it can lead to long waiting times for processes that arrive later.

Average waiting time is calculated by summing the waiting times of all processes and dividing by the number of processes. It indicates the average time processes spend waiting in the queue before being executed.

Average turnaround time is calculated by summing the turnaround times of all processes (completion time minus arrival time) and dividing by the number of processes. It represents the average time taken to complete a process.

First fit is a memory allocation algorithm that allocates a process to the first available partition that is large enough. It is simple and fast but may leave fragmentation in the memory.

Best fit is a memory allocation algorithm that allocates a process to the smallest available partition that is large enough. It aims to minimize fragmentation but is more complex than first fit.

A directory structure is a hierarchical organization of files and directories, allowing for efficient management and organization of files within a file system. It provides a logical way to categorize and access information.

Deadlock prevention aims to prevent deadlocks by enforcing mechanisms that eliminate the necessary conditions for deadlocks. It involves techniques like preventing mutual exclusion or preempting resources when needed.

Deadlock avoidance involves analyzing the current system state and resource requests to determine if granting a request could lead to a deadlock. It avoids deadlocks by choosing resource allocation strategies that ensure the system remains deadlock-free.

A system call is a request to make a specific action on the operating system. It acts as an interface between an application and the operating system, allowing the application to access system resources and perform operations.

Deadlock is a situation where two or more processes are blocked indefinitely, each waiting for a resource currently held by another process. This creates a circular dependency that prevents any process from proceeding.

The necessary conditions for deadlock are: mutual exclusion (only one process can access a resource at a time), hold and wait (processes hold resources while waiting for others), no preemption (resources cannot be taken away from a process), and circular wait (a cycle of processes waiting for each other).

Deadlock detection is a technique used to detect whether a deadlock has occurred in a system. Algorithms are used to analyze the current state of processes and resources to determine if any process is blocked indefinitely.

Starvation occurs when a process is repeatedly denied access to a resource it needs, even though it's eligible for it. This happens when the scheduler gives preferential treatment to other processes, causing certain processes to be starved of resources.

A batch operating system processes tasks in batches, typically from a queue, without user interaction. It's efficient for repetitive tasks but lacks interactivity and real-time responsiveness.

Burst time refers to the time a process needs to execute its task. This is the time the process actually spends using the CPU.

Response time refers to the time taken for the operating system to respond to a user request. It reflects how quickly the system acknowledges a user's action.

Static loading involves loading all the program modules into memory at the start of execution. It is simple but inefficient for large programs and can waste memory.

Dynamic loading loads program modules into memory only when they are needed, improving memory efficiency and reducing startup time. It allows using larger programs and accessing modules only when they are required.

File attributes refer to the information associated with a file, such as its name, size, type, creation date, permissions, and owner. They provide metadata that helps manage and identify files within the operating system.

A process is an active instance of a program, encompassing its code, data, and execution state. It's the unit of execution managed by the operating system, while a program is a static entity containing instructions and data that can be executed by a process.

Paging divides the memory space into fixed-size units called pages. Processes are also divided into pages and are loaded into available page frames in memory.

A page fault occurs when a process tries to access a page that is not currently in memory. The operating system then fetches the missing page from secondary storage (disk) and loads it into memory.

LRU (Least Recently Used) algorithm selects the page that was used least recently for replacement during page replacement. It assumes pages that have been recently used are more likely to be used again, but can be problematic for programs with irregular access patterns.

SCAN is a disk scheduling algorithm that moves the disk head back and forth across the disk surface, servicing requests in order. It's more efficient than FCFS but can cause longer wait times for requests on the opposite side of the disk.