Questions tagged [operating-systems]

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

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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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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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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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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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1answer
27 views

memory storage of a program before compiling

Whenever 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 ...
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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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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
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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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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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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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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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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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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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Context switch in an Text Editor

I am new to operating systems and have been wondering about this. Consider a normal text editor, and it's process running in the CPU. Since text editors include IO operations, do the process keep ...
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page table size in a 1 and 2 levels page table

Consider that virtual page numbers are 36 bits, and page table entries, as well as pointers to other page tables are 4 bytes each. First , if we need to calculate how much memory would a single level ...
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37 views

Operating Systems - Page Table - Address Translation - Physical Address & Logical Address

Hi, I am learning about memory management in operating systems. I am confused with Address Translation. In this question (pic attached), can anyone explain, how the answer is obtained for Blank #2? ...
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How can 4 GB of data can expand into 40 GB of data, when I install Windows on a Computer

Say I start with an iso with about 4GB of data and use this, to install windows on a computer. After installation, the operating system will take up about 40GB of disk space. Where does all this &...
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1answer
31 views

How multiprocessing is done in Single Core Systems?

Can we do multiprocessing on single core system ? I thought that single core means that ONLY one process/thread can execute at any time. For multiple processes , there can be concurrent execution to ...
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What is the difference of Process synchronization management between Windows and Linux?

I am looking for some explanation about process synchronization management in windows OS and Linux OS and what they do about the critical section and mutual exclusion. I will be so grateful if someone ...
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Understanding Cyclic Dependencies when using Soft Update for Filesystems

We recently delved into the concept of "Soft Updates" as a mean of maintaining a Filesystem as consistent. The solution, as we learned it, calls for 3 basic rules: We'll create a pointer to a file ...
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46 views

Difference between process contention scope and system contention scope

According to my understanding the difference between them is that in process contention scope there is a contention within the process for mapping user threads to kernel threads and for system ...
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Is process address space part of Process Control Block(PCB)?

I recently read about the process address space and PCB and trying to link them together. I don't find much literature on their relation. Is the process address space a part of the PCB data ...
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1answer
21 views

Real-time systems and real-time operating systems

Just to understand the topic a little bit better, I would like to know if there is a difference between real-time systems and real-time operating systems. I know that a real-time system is a system ...
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35 views

Is there any operating system running in Graphics cards?

Taking an example of NVIDIA graphic cards, is there a dedicated OS running on the Graphic card's GPU or the Host machine's ...
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1answer
21 views

Process synchronization problem

The atomic fetch-and-set x,y instruction unconditionally sets the memory location x to 1 and fetches the old value of x in y without allowing any intervening access to the memory location x. Consider ...
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33 views

Hierarchical page tables with page size of 8 KB

Consider a machine with a physical memory of 8 GB, a page size of 8 KB, and a page table entry size of 4 bytes. How many levels of page tables would be required to map a 46-bit virtual address space ...
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1answer
44 views

How to find a condition which leads to deadlock in non-reentrant locks

A multithreaded program P executes with x number of threads and uses y number of locks for ensuring mutual exclusion while operating on shared memory locations. All locks in the program are non-...
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50 views

When is it best to use the second chance replacement algorithm?

I'm going through 'Operating Concepts' by Silberschatz, Galvin and Gagne (The Dinosaur Book) and it mentions the Second-Chance Algorithm (not enhanced) as an improvement on the FIFO replacement ...
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74 views

Why are special instructions used to implement system calls? Why not use normal subroutine calling instructions?

The transfer of control is often completed through some type of software interrupt instruction. These special instructions result in the CPU to save the current state of the machine and transfer ...
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1answer
35 views

Is physical pages zeroed out before it's mapped to a virtual page?

I don't how this works. According to me if the physical memory is not cleared then there is some security risk as there may be some sensitive information in it from the other processes. How does the ...
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2answers
45 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
70 views

Difference between *device descriptor* and *device handler*

I am studying Computer Architecture, and am a bit confused about the difference between device descriptors and device handlers in operating systems. Am I correct in saying that a device handler is ...
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Calculating max file size

The question is "For a file system with 11 direct blocks, 5 indirect blocks, 2 secondary (double) indirect, 2 triple indirect blocks calculate the maximum file size allowed if block size is 2048 in a ...
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1answer
70 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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1answer
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NRU: Page fault on writing?

I am trying to understand the concept of NRU from the following link. I have got some problem in understanding the text below: NRU page replacement Algorithm If the hardware does not have these ...
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1answer
32 views

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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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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Preemptive priority scheduling problem with same priority

So if T1(priority 3, arrived first) was preempted it is put back to the runqueue. If there is already T4(priority 3, arrived fourth) inside the runqueue, which one of these two will be handled first?! ...
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1answer
99 views

What is cold-start penalty ? What are some ways to reduce it?

when a new process is created using a fork() function, there is a cold start penalty, what is this and why does it happen?
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Spin-Lock and Busy-Wait

This question has been asked and the top answer https://stackoverflow.com/a/38173155/12862537 is not satisfactory. So, it would be nice if someone could specifically point out the similarities and ...
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Android apps IPC during navigation of activity

During navigation of activities in an Android app by clicking back button, the current activity is paused, the previous one is restarted and resumed and the former is stopped. How does activity ...
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279 views

Can a TLB hit lead to a page fault?

$Can$ $a$ $TLB$ $hit$ $lead$ $to$ $a$ $page$ $fault?$ My answer is yes, as say even after a TLB hit if the page in the memory is dirty and it will lead to Page fault. Other case can be that, it is ...
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Message passing inter process communication

I was reading a book on OS by Galvin. I well understood that blocking send will wait until it has loaded the message into the kernel buffer. In contrast, the non-blocking send system call will return ...
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37 views

How are Operating systems involved in execution of programs?

By my understanding, operating system is the abstraction layer above hardware. Which means that an operating system that supports two different CPU architectures can run the same code. But I still ...
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19 views

Another feasible way to implement multi-level page table?

The advantage of a multi-level page table is that we can swap the inner-level page tables to some secondary storage. If however we want quick access to the whole address space, we have to keep all ...
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192 views

what is the difference between an adapter and a controller?

1- why do have a USB controller but a display adapter ? 2- I have heard the terms network adapter and network controller being used, is there a differance between those ?
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working set bits in working set approximation

I am looking at the example pdf from Cornell found here: https://www.cs.cornell.edu/courses/cs4410/2016su/slides/lecture13.pdf Also reading OS Concepts 10e Chapter 10 but it does not go into detail. ...
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Operating System scheduling

I was reading a book on Operating System by Galvin and came across this : In the latest version of Solaris, scheduling is controlled by loadable tables. Depending on the table currently loaded, the ...

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