Questions tagged [operating-systems]

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

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43 views

Is “capability-based security” vs “hierarchical-protection-domain based security” a false dichotomy?

The wikipedia page on capability-based security states: Capability-based security is to be contrasted with an approach that uses hierarchical protection domains. However, in order to implement ...
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Regular OS Vs RTOS

I am curious to know if RTOS provides deterministic scheduling gurantees then why not all OS'es are RTOS? In what sense regular OS say linux better then RTOS say FreeRTOS?
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OS: Are User-level threads and software threads (and also kernel-level threads and hardware threads) the same?

I am referencing the Book Fundamentals of Computer Algorithms" by Ellis Horowitz et al. At the part which they talk about multi-threading models, user-level and kernel-level thread are introduced....
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Does the host operating system know the content of your messages in a messaging applications?

Let's say you are using a messaging application (Microsoft Team, Skype, Telegram,..) on an operating system (Windows, MacOS, Linux). Does the OS know what you are sending or receiving? If yes, how? ...
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Why do we need hashed page tables for Paging in Operating Systems?

I understand that we might need hierarchical paging to handle page tables with sizes greater than the size of one frame, but what is the use of Hashed Page tables then? I would understand if we were ...
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Is logical to physical address conversion inclusive?

If I am trying to translate a logical address of page N and offset O, and my translation unit tells me the translation has a base address of B and a length of L, is the length L inclusive or will it ...
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114 views

Is logical address generated by CPU and MMU same if Physical and Virtual address space are same?

The system has same physical and virtual address space i.e. 32-bit. Are the logical address generated by CPU and address generated by MMU same?
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25 views

Multi-level paging where the inner level page tables are split into pages with entries occupying half the page size

A processor uses $36$ bit physical address and $32$ bit virtual addresses, with a page frame size of $4$ Kbytes. Each page table entry is of size $4$ bytes. A three level page table is used for ...
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144 views

Questions regarding CPU scheduling algorithms ( Round Robin and Priority scheduling )

Consider the following processes : 1) My First Question is if we need to schedule them using preemptive priority scheduling with Round-Robin for equal processes priorities with a quantum of 3. Here ...
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2answers
628 views

Convoy effect in priority scheduling and SJF (Non preemptive)

In books, I have read that FCFS suffers from convoy effect. I think that even SJF and priority(both preemptive and non preemptive) can suffer from convoy effect. In SJF, if a process with large burst ...
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1answer
67 views

Is vmlinux a virtual machine?

From Wikipedia, On Linux systems, vmlinux is a statically linked executable file that contains the Linux kernel Does that mean vmlinux is a virtual machine that runs Linux? I am really confused.
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955 views

LRU vs FIFO page replacement

I am wondering if there is an instance where FIFO results in less page faults than LRU. For example: 2,6,5,7... In this string, if I have to complete it by ...
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1answer
59 views

Algorithm favours CPU bound or I/O bound processes

Some scheduling algorithms favour CPU bound processes while others favour I/O bound processes. Which algorithm favours which type of process? My answers: SJF favours I/O bound processes.Explanation: ...
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Making sense out of byte-order in text

I have stumbled about the way a text file is saved by the OS. I have typed: printf "ab" | hexdump and the output was: 6261 which are the letters in reversed ...
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1answer
117 views

Task scheduling algorithm that limits concurrency

My prof introduced us an algorithm with semaphores that was used to solve the "dining philosophers" problem. The algo is ok, apart from that it limits concurrency. What does mean that it "limits ...
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How does an operating system implement the C library?

I have an idea of how a C program is turned into machine code by the compiler. I also know how the processor processes the instructions (https://www.youtube.com/watch?v=cNN_tTXABUA this video has a ...
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5answers
2k views

Operating System - CPU scheduling Decisions

I understand that CPU scheduling takes place on 4 circumstances listed below: When the process changes state from Running to Ready Changes state from Running to Waiting Changes state from Waiting to ...
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231 views

What does this mean: “The compile-time and load-time address-binding methods generate identical logical and physical addresses”?

I read this in my Operating System textbook. Does it mean that the logical addresses generated by compile-time binding scheme are the same as the logical addresses generated by load-time binding? Or ...
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2answers
544 views

Does throughput includes CPU idle time also?

I have 3 processes P1,P2,P3 having gantt chart as follows => Now, CPU remains idle in 0 - 2 sec and 44 - 47 seconds as I/O is taking place. Does, this affect throughput as 3 processes can be ...
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1answer
168 views

How can i draw a general resource graph which cannot be completely reduced but which is free from deadlock?

How can i draw a general resource graph which cannot be completely reduced but which is free from deadlock? A general resource graph which can be completely reduced and hence is free from deadlock is ...
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35 views

• How CPU identify that which device is sending the request? • How CPU decide which action should be taken for each request?

• How CPU identifies which device is sending the request? • How CPU decide which action should be taken for each request?
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21 views

Deadlock still occurs

Is it in in a deadlocked state? In this graph, there is a deadlock initially I think. Since P1 is holding R1 and waiting for R2; P2 is holding R2 and waiting for R1 and R3; P3 is holding R3 and ...
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4k views

Operating Systems - SJN/Round Robin - turn around time + waiting time

2.(10 pts) a) You are given 4 processes in a batch system that all arrive at time 0 with the following CPU burst times: P1 : 35, P2: 25, P3: 13, P4: 22. Assuming there is no context switch ...
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9 views

How to enforce synchronization with two semaphores

Assume I have 4 threads, A B C D respectively. A finishes before B starts. B finishes before C or D start. How should I initial values and synchronize threads with 2 semaphores?
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1answer
49 views

Flow of control when calling a function

I am learning about embedded and operating systems. I would like to know the order of control flow that occurs when a user-space C application calls a function, for example, printf(). I am slightly ...
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Exception handling

In problem 1 part D) of https://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-004-computation-structures-spring-2017/c17/c17s3/os_answers.pdf, how come process 1 is never scheduled?...
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2answers
116 views

Determine page number and offsets for address references

I'm working on learning operating systems and I've come across a strange question that I don't know how to answer. The question is: Assuming a 1-KB page size, what are the page numbers and offsets ...
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1answer
47 views

Why does an inverted page table keep a chain of pages per frame when it can only store one of such pages?

I'm currently dealing with inverted page tables and how they work. If I understood correctly, an IPT is a table that maps a frame number to a PID and page number. The way this works is by having a ...
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1answer
475 views

Difference between present - absent bit and valid - invalid bit in a page table?

while reading I found this: Present/Absent bit – Present or absent bit says whether a particular page you are looking for is present or absent. In case if it is not present, that is called Page ...
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25 views

Simultaneous buffer access in the bounded buffer problem

Galvin and various other resources only allow either the producer or the consumer to access the buffer at a time, the common code is as follows: ...
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2answers
43 views

How a swapper manipulates entire processes in the operating system?

The below-given lines are written in the book of the operating system (Page -307), details of the book are as follows: OPERATING SYSTEM PRINCIPLES, 7TH ED., Abraham Silberschatz, Peter Baer Galvin, ...
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1answer
71 views

How do computers really communicate with hard-drives on x86_64?

All of us have saved a file on our computers using a programming language. If I look down through the layers of abstraction, I usually get stuck at a kernel-level call or a C-call like ...
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IoT OS running on top of Ubuntu?

I am new in the field of IoT OS and I saw TinyOS, Conitki etc. can be installed on top of Ubuntu. Its not clear to me how these OSes are able to run on top of Ubuntu without any Hypervisor? Can ...
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What is a student process?

According to Galvin and Silberschatz, 5 queues are maintained in multilevel queue scheduling, each for: System Process Interactive Process Interactive Editing Process Batch process Student Process ...
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Why do OS locks require hardware support?

I just read the chapter on locks in the book Operating Systems: Three Easy Pieces, and it discusses an implementation of locks (see in Figure 28.9) that involves a test-and-set hardware instruction. ...
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1answer
506 views

Does starvation freedom imply progress?

The above answer taken from the book https://www.amazon.com/Operating-Systems-Sibsankar-Haldar/dp/8131730220 says starvation freedom may not imply progress as processes can be deadlocked. I think ...
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1answer
80 views

Early Deadline First (EDF) scheduling in real-time systems feasibility test proof

I am trying to prove Theorem 6.2 on page 127 of the book Real-Time Systems by Jane W. S. Liu: http://www.cse.hcmut.edu.vn/~thai/books/2000%20_%20Liu-%20Real%20Time%20Systems.pdf It is based on Early ...
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2answers
19k views

Changing from Kernel mode to User mode (and vice versa)

I am reading Operating Systems book by Galvin. Galvin explains, what are kernel & user modes, instruction privileges given for both modes & also about mode-bit. But I am interested to know how ...
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61 views

What does starvation freedom exactly mean?

Galvin offers the following definitions of starvation: Indefinite blocking, or starvation, a situation in which processes wait indefinitely within the semaphore. A major problem with priority ...
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54 views

How were operating systems even made?

By that, I don't mean what is needed to make an operating system. I know that OSes are built on top of kernels and whatnot. But what I mean is, it wasn't like anyone could just "program" the ...
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13k views

How to compute total internal and external fragmentation

I want to find the total external and internal fragmentation. What I understand is that external fragmentation occurs when processes are loaded and removed from memory, causing memory to be broken ...
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5k views

How to calculate average waiting time for round robin cpu scheduling?

I have tried to calculate average waiting time for the below details there are two answers I'm getting using two methods I'm not understanding which one is correct? The time quantum is 2 This is the ...
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1answer
97 views

Default scan order in SCAN and LOOK disk scheduling algorithms

I've been learning various disk scheduling algorithms in Operating systems. I wanted to know if there was any default scan order in SCAN, C-SCAN, LOOK and C-LOOK algorithms, like towards higher ...
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1answer
49 views

Does Dekkers solutions to critical section problem ensure progress?

I was reading concurrency control section from Operating Systems book by William Stallings. In this book, he gives three attempts by Dekker to give solution to critical section problem: Attempt 1 <...
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I want to learn more about computer science. Where should I start?

Hello computer scientists, I am a mathematician. I have taken some undergraduate courses in C++, Python, assembly language, boolean algebra, logic, graph theory, etc. I would like to learn more about ...
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510 views

Paging: Does the page table of a process also gets swapped out when the process gets swapped out from main memory?

Does a process's page table too gets swapped out to secondary storage from main memory when the process gets swapped out to secondary storage from main memory? And gets swapped back in when the ...
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9 views

the difference between Idle point and Idle slot

I believe that I don't understund well the difference between an idle processor point and an idle slot Thanks
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45 views

Gantt chart for Round Robin Scheduling using only arrival and completion time

I had the following question in my Operating System 'CPU- Scheduling' assignment- 4 processes A,B,C,D have estimated time of completion of 5,7,9,11 ns each. They are scheduled in a round-robin fashion ...
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47 views

Confused between the terms Process and Process Control Block

I was reading about the Long term scheduler, when I read that when memory is not enough and load on the CPU due to multiprogramming is too high, a process might be moved to secondary storage space (...

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