Questions tagged [operating-systems]

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

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Starvation and Livelock

I think Option C is false. Following is my thought process: Starvation in general mean Process is waiting indefinitely for the resource or to get scheduled etc. [A/c to Galvin Book]. So, here in this ...
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6answers
549 views

Representation of unsigned integer on a little endian, big endian computer

This is a GATE 2021 exam question. If the numerical value of a 2-byte unsigned integer on a little endian computer is 255 more than that on a big endian computer, which of the following choices ...
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What is a job queue? [duplicate]

I have a hard time understanding the concept of job queue. For example, when a user clicks the icon of an executable, the newly created process is passed to a job queue, and the long term scheduler ...
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33 views

Is it okay to understand Job Queue Like this?

I have a hard time understanding the concept of job queue. Is it right if I understand job queue like the following??? For example, when user click the icon of an exe file, the newly created process ...
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1answer
25 views

Question about pointer in PCB structure and meaning of job queue

PCB structure exists inside kernel area. And in ready queue, which is Linked List, each Node of the queue is PCB. And this mean PCB Node has the next address of PCB in the queue, right?? Then My ...
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15 views

Page fault rate while calculating effective access time

So here is a question regarding calculating effective access time (EAT). So the question is : suppose a system with an average page page-fault service time of 6 milliseconds and a memory access time ...
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23 views

Different ways to avoid deadlocks

I am thinking of techniques that we can implement in order to avoid deadlocks in processes. While I am aware of some tactics, e.g. killing a process when we reach a deadlock, or using spooling, would ...
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1answer
33 views

How are semaphores and test-and-set instructions connected?

Cheers, so my textbook explains these parts very poorly, so I would gladly take any advice! I am confused between the test-and-set instructions, which per my book is a very common CPU instruction set, ...
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Minimal number of resources such that the system is considered safe?

In a system with a single type of resource, there are 8 processes with the following maximal requirements: Process P1 P2 P3 P4 P5 P6 P7 P8 MAX 75 60 65 35 30 45 30 30 Specify the minimal value for ...
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30 views

How many different values can a shared variable take in concurrent computing?

Question: Is there a way to find out number of different values that a shared variable can take in concurrent computing, in general, without listing all the possibilities and then counting the ones ...
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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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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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2answers
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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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1answer
153 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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• 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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23 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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10 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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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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1answer
73 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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1answer
48 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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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
53 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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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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107 views

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
83 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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1answer
56 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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1answer
65 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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1answer
49 views

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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79 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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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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52 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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1answer
54 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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why you couldn’t use mmap to manage a rdbms buffer pool - or the whole rdbms itself just like NoSql stores?

why you couldn’t use mmap to manage a rdbms buffer pool - or the whole rdbms itself just like NoSql stores? I see that Cassandra, Hbase, Elastic do use mmap so why not use the same strategy for an ...
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Round robin doubt

Consider a system running ten I/O-bound tasks and one CPU-bound task. Assume that the I/O-bound tasks issue an I/O operation one for every millisecond of CPU computing and that each I/O operation ...
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Operating system scheduling doubt

Consider a uniprocessor system executing three tasks T1,T2 and T3 each of which is composed of an infinite sequence of jobs (or instances) which arrive periodically at intervals of 3, 7 and 20 ...
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64 views

Why can't we compile 8086 Assembily for all OSs from any OS?

If Mac OS, Linux, and Windows (mostly) all use Intel's 8086 64 bit instruction set, why can't we compile 8086 64 assembly from any operating system to any other operating system? (e.g. compile a Mac ...
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23 views

A 32 – bit wide main memory unit with a capacity of 1 GB is built using 256M X 4-bit DRAM chips

A 32 – bit wide main memory unit with a capacity of 1 GB is built using 256M X 4-bit DRAM chips. The number of rows of memory cells in the DRAM chip is 2^14. The time taken to perform one refresh ...
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44 views

Storage in registers

Whenever CPU needs the data, it gives the address of that word to the RAM via bus, then the RAM generated the copy of that word and sends to the registers via bus. Why can't the RAM send the original ...
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3answers
154 views

How is a program stored before compiling?

When we write code, after compilation the code will be converted to machine language and then stored in the hard disk. But before compiling the code, it is still in the high-level language. How and ...
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29 views

Do all processes are allocated equal sized page map tables?

I have a simple question : In a paged memory system, all processes are allocated equal sized page map tables ?
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28 views

Question regarding the one and two level paging system

I am studying for my OS final exam and I am solving some problems related to virtual memory . however , I have faced a problem which I need to test my understanding regarding it : ...
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1answer
53 views

Paging only for user code. What about kernel code?

Why is paging done only for user code (user space)? I know that the basic intuition behind paging is for managing larger logical address space in smaller physical main memory space. Won't the kernel ...
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10 views

PSH flag in TCP header send a singal to the receiver process?

we know that when TCP data is received with PSH set, it will immediately transfer the received data to the application.and let's when pushed data arrives the receiver side and the receiver application ...
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28 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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How to calculate the size of the page table of a process?

Consider a system with A bytes of physical RAM, and B bytes of virtual address space per process. Pages and frames are C bytes in size. Every page table entry is P bytes in size. Calculate the size of ...
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64 views

Can User Level Thread read/write Kernel thread?

As far as I read in a OS text book (Operating Systems by Silberschatz) Kernel mode is for privileged task, so it it true to claim that "User Level Thread can read/write Kernel threads" ? ...
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3answers
65 views

How does the OS handle multiple stacks in its physical memory?

Without assuming ASLR... Processes have virtual addresses, and they manage stacks & heaps of their own. However, these all get mapped to physical addresses somewhere on the memory. Let's say we ...
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1answer
38 views

Can application DNS requests bypass a firewall on Windows and Linux

Assuming I have firewall set to block an application from accessing the Internet, would I DNS request go through? I tried using C (gethostbyname) on Windows and the answer is no. It seems that the ...

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