Questions tagged [operating-systems]

Questions about the principles of software that interfaces between hardware and applications.

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Timesharing and the MMU

Imagine we are running a program on a modern operating system, such as Linux or Windows. After running for some time, the program's time slice is up. A different program (process) starts to run again. ...
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Mathematical models of computation that capture more advanced OS and CPU design features

The universal Turing machine is the standard theoretical model of a stored-program computer. While in one sense as general as possible (Turing completeness), it doesn't explicitly contain many of the ...
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Differences between reliability and availability using an example

My definitions of reliability and availability are as below respectively . reliability := property of failure interval . availability := property of occupancy rate . I want to show the differences ...
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CPU utilization estimation

In the Modern Operating System by Andrew Tanenbaum, Herbert Bos the authors provide their explanation of the concept of CPU utilization in the following way: A better model is to look at CPU usage ...
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Incorrect average turnaround time calculated for FCFS schedule?

I am trying to solve the following problem: If all of the jobs listed below are scheduled FCFS (First Come, First Serve) with no switching overhead, the average turnaround time is going to be: ...
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Deadlocks: Why if 2 threads are waiting for a lock from each other results in a deadlock?

I am confused as to why 2 threads waiting for a lock from each other will result in a deadlock. Let's say I have a Thread 1 that needs to execute contents in Lock 1 and then Lock 2 and a Thread 2 that ...
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What is the need for Kernel threads?

I'm a bit confused about kernel-threads, I searched a lot at the Internet, SOF and here but found very diverse and conflict answers. What is the need for Kernel threads? Are they threads that are only ...
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Over the course of history, did Linux and Windows NT kernel design learn from each other?

Linux Kernel in its primitive form was first written in 1991; Windows NT kernel (differ from Win9x Kernel which was based on DOS) purportedly began development in 1990. both being a monolithic kernel, ...
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Why semaphores lead to loss of modularity?

In this article Semaphores in Operating System and other articles on the internet, they have mentioned one of the disadvantages of semaphores is that it leads to loss of modularity. They further said ...
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What happens when I open a file? Is a temporary copy of the file created?

When I open up a file two different editors, vscode and sublime, changes saved in vscode are visible directly in sublime text. Same doesn't work with nano text editor. Any help?
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How does the Linux kernel build its symbol lookup table?

I am writing a small x86-64 OS. I am trying to make sense of how Linux loads modules at runtime by linking them into the kernel. I understand that Linux builds a symbol lookup table. Basically, a ...
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What are the major functions that are performed by CPU to handle the I/O devices?

I can't find the complete answer from browsing that's why I am asking. I found functions of IO interface. Is it the complete answer for this question? Hope I can get some pdf of website links from ...
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How is segmentation a solution to external fragmentation

As per Galvin's book, segmentation is the solution to external fragmentation. But in segmentation, the memory blocks are of different sizes. So, if one segment is removed that creates a hole. If we ...
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What are the minimum functions, services, or features of a software to be called as an operating system?

When can we say that a software is an operating system and not a firmware, in terms of what it can do? I know that firmware is usually stored in ROM and OS is stored on HDD/SSD, but technically you ...
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How could a page be invalid in demand paging?

I was reflecting on what I learned about demand paging and I have a question: In demand paging, we have entries in the page table only for frames that are present in physical memory. So I was ...
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Why does page size affect page table size?

I am revising operating systems theory (I'm Italian, forgive me for bad English) and there is a slide that states: If page size is small then we avoid internal fragmentation (I get that) but we have ...
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Understanding how internal fragmentation occurs in systems using only paging with huge page size

The excerpt below is from the OS text by Galvin et. al. When we use a paging scheme, we have no external fragmentation: any free frame can be allocated to a process that needs it. However, we may ...
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disadvantages of a long time quantum in scheduling

I'm trying to understand the example showing disadvantages of a long time quantum in Tanenbaum's book in Section 2.4.3 “Scheduling in Interactive Systems”. To improve the CPU efficiency, we could set ...
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When are a controller's registers loaded and ready to inform an I/O Operation?

Below, I appended a fragmented paragraph from Operating Systems Concepts on interrupts. To start an I/O operation, the device driver loads the appropriate registers in the device controller. The ...
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How LRU is used without special hardware?

I had been curious as to which page replacement algorithm is used in OSes like Windows and Linux. I could find that most information on the internet pointed at LRU(Least Recently Used) Algorithm. But ...
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Are Paging and page cache the same in Operating system?

I was looking at paging in OS. It seems like there are two concepts with the same name but with different features, and I wanted to be clear about those, Paging and page cache. Before I thought paging ...
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1answer
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Are pages moved to the disk when the process is scheduled?

When process A has run long enough and the scheduler decides to run process B, will all the pages of process A be moved to the disk or they remain in the main memory?
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Where will the TLB entries be stored if the cache memory get full (or can this situation occur)?

As we know that the entries of the TLB get copied into the cache memory once another process is chosen to be run by the scheduler. But what if the cache memory is full and there is no space left for ...
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LONG TERM SCHEDULER and how does it interact with USER

If I select chrome browser, then I select Android Studio, do they directly open in Ready Queue (allocated to RAM main memory), what processes actually goes into job queue? Does Job Queue gets filled ...
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Are the number of entries in the TLB(Translation Lookaside Buffer) limited?

If not, then why aren't all the pages loaded into the TLB so that TLB misses never happen.
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Is whole OS copied to ram when running?

If so, for any OS more than 10gb, how does it run on a computer with limited ram like 4gb? If not, which part of OS is copied to the ram? Or is it dynamically loaded whenever certain part is needed?
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Whats the difference between baremetal and full-featured in Embedded Systems?

Our professor talked about the "two" types of embedded systems in today's lecture, listing these. 1.) Baremetal 2.) Full-featured Now I found out what he means by baremetal, but I can't find ...
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Where are process pages stored - in the swap space or under file system? Can demand paging work without space space?

The Galvin OS text says that on older systems, there used to be a method, where the entire running process (when in idle state) was moved from the main memory (when main memory ran low) to the disk ...
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Starvation in Dekkers Algorithm

In the dekkers algorithm for the critical section problem, I happened to have come across a scenario in which P0 can starve out P1 in accessing the critical section(CS)(This is not an assertion, This ...
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concurrency vs parallelism

I am so confused between concurrency vs parallelism in multi-core processors. If a concurrent process has many threads and if the processor is multi-core then can each thread run on multiple cores? If ...
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Prove correctness of a solution to the critical section problem in general?

I was wondering if there is any formal, general way to prove the correctness of a candidate solution to the critical section problem in synchronization. For example, in the image enclosed, I have ...
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concurrency in multiple core

I know the basic definition between parallelism and concurrency. But there is not much information about concurrency in multiple core. what is the difference between concurrency in single-core vs ...
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What happens if there is context switch while executing system call?

Suppose a process does system call, hence it goes to kernel mode, the registers are saved. Now the system call will be running in process' allocated kernel stack. Can there be a context switch when a ...
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Process Scheduling (SRTF)-

Consider a uniprocessor system with four processes having the following arrival and burst times: (i) Calculate the average waiting time and also the average turnaround time if shortest (remaining) ...
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What does it mean that Atomicity is composable?

I'm reading a book from Michel Reynal called Fault-Tolerant Message-Passing Distributed Systems. In chapter five of the book, The Read/Write Register Abstraction, I have a few questions. On page 85, ...
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How does a command interpreter/Shell recognize a command?

I want to know when we enter a command in a shell then how does the computer recognize that command? Does it match that command with something already stored in files?
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How do you work out the segmentation table, offset and frame size in segmented memory management?

If I had a process, 1, which has the following segments: Segment 1 - 50 bytes Segment 2 - 200 bytes Segment 3 - 90 bytes and I know that the total bytes in memory is 1024, how do I work out the offset/...
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Confusion about the definition of "Exponential Average"

I was having doubt regarding the concept of "exponential averaging". Till now I have come across the concept twice and they seem to be quite similar (except that they have minor but sharp ...
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In Round-Robin Scheduling with $n$ processes in ready queue and time quantum $q$, each process gets $1/n$ of CPU time in chunks of at most $q$

I was going through the Round-Robbin Scheduling Section of the dinosaur book by Galvin et. al. where I came across the following statement by the authors: If there are $n$ processes in the ready ...
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Difficulty in understanding the "expontential average" plot of the estimate of the next CPU burst with the actual CPU burst

I was going through the portion of exponential averaging (to find the CPU bursts) under Shortest Job First (SJF) Scheduling from the dinosaur by Galvin et. al. Let $t_n$ be the length of the $n$th ...
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In Operating Systems, I can't understand why deadlock happens, why does a process not let go of a resource when it is done using it?

I know deadlock occurs when Process A has resource R1 and is waiting for resource R2, while process B has resource R2 and is waiting for resource R1, however why don't both processes just let go of ...
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Is the kernel loaded into memory for every user simultaneously using a Multi-User O.S. system?

I have a doubt about loading kernel for every user using a Multi-User system. Every user's processes and programs are scheduled to CPU in a time-sharing fashion. But, do every user on the multi-user ...
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How to determine memory allocation for single level table

I received this problem on my study guide but I have no idea if I'm doing it correctly: How much space needs to be allocated for a single-level page table for a machine with a 32 bit virtual memory ...
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(reference) Where can I learn more about I/O operations in OS?

I have basic understanding of file I/O. I know how to operate the read and write system calls in Linux. I know that there is blocking and non-blocking I/O. I want to know more about the underlying ...
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What exactly is execution-time address binding?

According to these two definitions: Logical address: every memory address generated by the CPU. Physical address: address which identifies uniquely a (real) memory cell. my textbook (Operating ...
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How could one construct a TLB so that not all the bits of the presented address need match to result in a hit?

I was wondering besides the typical matching of all bits in the presented address to the resulting page, is there another way of doing so? what are the benefits/ cons and how would one go about doing ...
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What is meant by a single-threaded kernel?

I was looking at this course but I cannot seem to understand what is meant by the term "single-threaded kernel". Does it mean that: only a single kernel thread is made available by the OS? ...
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CPU scheduling Decisions

Operating System - CPU scheduling Decisions The question above talks about why CPU scheduling does not take place when ready to running. But I wonder why CPU scheduling does not take place when new ...
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Page Size, Physical Memory Size, max Program Size

In a 64 bit computer, the logical address space is 64MB and physical memory size is 2GB. Paging is implemented with 4KB pages. Determine the logical and physical address components. (That is, how many ...

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