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Questions tagged [operating-systems]

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

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Multiprogramming within a paged system

So lets say that have a system with a PMMU that supports 10 bit physical addresses, and its processes are only able to use 8 bit logical addresses. The page size is 64 byte and the word size is 1 byte....
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Persistent Memory Emulation Platform (PMEP) [on hold]

How can I access to Persistent Memory Emulation Platform (PMEP)? It is supposed to be designed by Intel to simulate Non-Volatile Memory. It's mentioned in a few articles but quite unclear how to get ...
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Explain in laymen terms - How do modern programs translate into machine code

I'm sure this will benefit anyone else on a computer science fundamentals back-fill journey.. I'm slowly learning Assembly and while I'm starting to understand the core of it (MOV, JUMP, etc) and can ...
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Why does transaction-end block in a data journaling have to be atomic?

I am reading File Systems Journaling(http://pages.cs.wisc.edu/~remzi/OSTEP/file-journaling.pdf) from the textbook Operating Systems: Three Easy Pieces and I cannot understand the following: On page ...
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1answer
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How the operating system allocated to dual-channels memory?

I learned that the boot loader transmit the operating system from Hard Disk to Main Memory during the booting process. I wonder, today's computers are equipped with multiple slice of memory of dual-...
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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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Addresses with no memory allocated

I've read that a program can crash if it tries to access addresses with no memory allocated. But, how is it possible that an address has no memory allocated? When does it happen?
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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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Appreciating the concept behind file reading from terminals [migrated]

I am starting out in Operating Systems module and these question really caught me off-guard. These questions have no solutions. (a) In Windows, start a command line shell, eg. cmd. Assuming that you ...
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1answer
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Appreciation of the 5 state process model

I'm starting out in an Operating Systems module. I have a few understanding questions to think about, which will not be gone through in class. A process state model is an abstraction (or model) which ...
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1answer
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Memory Mapping Segment

I read that "Memory Mapping Segment"/"memory mapped file" is a segment of the virtual memory of a process, where a file or file-like Ressource is loaded into. It is for high performance file I/O. I ...
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Two Process Solution for Critical Section Problem- Algorithm 1

I have started learning Critical Section Problem and its various solutions. To explain my question, let me first give a brief background of it. The general structure for a two Process Solution for ...
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address spaces of changing processes

I read that the mapping for user-space processes is changed after each process switch. By mapping I mean the translation from virtual addresses to "real" memory address. I thought that processes are ...
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1answer
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What does it mean " The outer level page table need not be page aligned?

The question is in context to multilevel page table. I was trying to solve numerical on multi-level paging and noticed that page size might not be same at all levels. I came across the point "Outer ...
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Difference between Response time, Execution time, and CPU time

I studied Computer Architecture from David A. Patterson and have came across the idea of Response time. Response time also called Execution time. The total time required for the computer to ...
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1answer
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multithreading - duration of jobs

" How long will it take for 2 jobs to complete if they're running in parallel, knowing that both have a total of 20 minutes of CPU usage time and 50% IO" I calculated the CPU usage: ...
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Calculate for each block, the number of bytes that can be assigned to data and to pointers to other blocks

In trying to solve the following problem: You are presented with the first 15 blocks of a secondary storage device (disk) which has a total of 30000 KB available. The linked allocation method is ...
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1answer
27 views

Threads and Operating System

In a computer, the processor executes different threads and changes between them, the operating system is a program at the end that it´s being executed by the processor, there exists the posibility ...
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If the string of N requests is repeated many times, which of the following is/are true?

If the string of N requests is repeated many times, which of the following is/are true? I. The fewest page faults occur when M ≥ N. II. LRU (least-recently-used) and FIFO (first-in-first-out) will ...
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1answer
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Round-Robin fashion exercise

In my Operating Systems class I have an exercise to sketch out how a round-robin algorithm would apply to a specific scenario, which is the following: Now the correction that I was provided with by ...
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Definition of multiprogramming [duplicate]

Which combination of the following features will suffice to characterize an OS as a multi-programmed OS? a. More than one program may be loaded into main memory at the same time for execution b. If ...
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interrupts in operating system

Normally user programs are prevented from handling I/O directly by I/O instructions in them. For CPUs having explicit I/O instructions, such I/O protection is ensured by having the I/O instruction ...
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1answer
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ARM STM instruction: page fault problem with MMIO

The ARM STM instruction is described here in the ARM manual. This instruction writes all or a subset of registers at memory locations starting from a base memory ...
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1answer
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Instructing operating system - Knowing it's functionalities

TL;DR: I would like to know how a programming language, the OS and drivers work together to perform a task. I (and we all) have used various softwares/modules/packages on the top of our OS which ...
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Who decides that process needs cpu time or not?

I wonder how does particular process gets CPU time or resources whenever it's required to execute some instructions? When a process is in the idle state or waiting for input, it's not occupying the ...
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1answer
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Is OS mode required for accessing general purpose registers

In which of the following cases a process executing in user model is required to enter into the OS mode? (a) Decreasing the value of unsigned integer value in a register to less than 0 (b) Accessing ...
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What should be the minimum value when the two threads are executed concurrently

int count=0; void *thfunc() { int ctr=0; for(ctr=0;ctr<100;ctr++) count++; } If *thfunc() is executed by two threads concurrently in a uniprocessor ...
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Relating L1 cache, TLB and main memory

Earlier while solving problems from computer organization book by Stallings, I came across the fact that $T_a=(H_{L1})(T_{C1})+(1-H_{L1})(T_{C1}+T_M)$ where, $T_a \rightarrow$ Average access ...
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How Does an Operating System/BIOS Determine Physical Addresses of Devices?

So I understand that in every computer, the Operating System, the BIOS, or both will determine the physical addresses of the hardware devices and then translate that into virtual addresses. What I don'...
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Deadlock vs “Progress” requirement of the solution to the critical section problem

I came across following problem: Consider following code: ...
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1answer
35 views

Cache and Main Memory

As we know that average access time is given by t=p*(tc)+(1-p)*(tc+tm) where t represent the average time, p is the hit ratio , tc is the time to access the data from the cache and tm is time to ...
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28 views

How can I implement locking a range of values in a sorted sequence?

I am trying to write a general purpose locking algorithm which allows me to lock a range of contiguous values in a sorted array. To start with, these could be exclusive locks - so two concurrent locks ...
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Number of memory cycles stolen for transferring one word

The storage area of a disk has the innermost diameter of 10 cm and outermost diameter of 20 cm. The maximum storage density of the disk is 1400 bits/cm. The disk rotates at a speed of 4200 RPM. The ...
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1answer
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In a kernel, what are “global constructors”?

I am a beginner developing kernels (though I have developed several Hello World programs in C and C++). I frequently see reference being made to global constructors (e.g., osdev https://wiki.osdev.org/...
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Why are threads called the unit of dispatch?

Threads called the "unit of dispatch" but what does that mean? I was looking over the web and two operating systems books but I can't find the answer. It seems that processes are defined by two ...
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1answer
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How does hashed inverted page table work?

I understand hash function and inverted page table, but then the book I read describes something called hashed inverted page table (use hash to accelerate the finding because IPT is large), with TLB ...
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Why is it difficult to differentiate between system and user CPU time?

In the book, Computer Organization and Design, Fifth Edition, by D. Paterson, it is stated that Differentiating between system and user CPU time is difficult to do accurately, because it is often ...
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If the number of pages exceeds the number of frames, how can the process finish using Virtual Memory?

Mapping is not for paging, is it? For instance if we have 12 pages and 8 frames. If 7 out of these 12 pages are loaded into the main memory, how can the process terminate?
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How is switching among user-level threads realised in the user space?

This is with respect to user-level threads where the kernel only knows about the process as a whole, and threads are created and maintained in the user space. Each thread has its PC, registers, stack ...
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pool of free page frames OS

I read that in a paging scheme memory management, some os's have a paging daemon that wakes up periodically to inspect the memory of the RAM. This is to ensure that modified pages can be scheduled to ...
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How can we compute how many processes should be in memory at a time to make CPU utilization max?

From the given formula, we can compute the CPU utilization: CPU Utilization = 1 - P^n Where p is the probability of I/O and n is the total number of processes. E.g, If we were to find CPU ...
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Determining the linear address

So I am working on a question that requires me to find the linear address. Here's some information: Main memory size is 8GB, which translates to $2^{3} * 2^{30} = 2^{33}$. Block size is 16KB each, ...
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Mutual Exclusion by disabling interrupt

I am reading William Stallings operating system book which gives this pseudo-Code for disabling interrupt to achieve Mutual Exclusion ...
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Longest Remaining Time first with Non-preemption

Below is a question from a quiz I attempted(for preparing for a competitive exam), I found the solution to be bit confusing and wanted to clear my concept. Below was the solution given I have a ...
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130 views

Which Peterson’s Solution is right?

I have seen two different Peterson’s Solution to mutual exclusion, one is from Modern Operating Systems: ...
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Why does the operating system switch an active process to different cores?

When running a single-threaded application that is 'always busy', on a multi-core computer, modern operating systems will typically switch the process from one core to another from time to time. Even ...
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1answer
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Are space allocated to C/C++ variables in secondary storage also in Compiled file?

Are data segments,heap,stack etc also present in secondary memory with compiled code then later mapped by OS to RAM when I open it?
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How can a user process even try to access a memory location its not allowed to when it doesn't have access to page table?

So is it even possible for a user process to even try to access a physical memory location that does not belong to it and therefore getting an error by operating system? because for example with a 32 ...
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How pictures and videos are usually loaded in Memory? [closed]

Lets assume I'm talking about Jpeg and Mp4 and a general video player(not sure if different ones load it differently, if they do please tell) So do video players (process) usually load the entire ...