Questions tagged [operating-systems]

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

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What's the official name of “New” page replacement algorithm?

I am studying some page replacement algorithms. I found an interesting algorithm called "New" algorithm. From page 17 of this slide (https://web.stanford.edu/class/cs346/2015/notes/Lecture_One.pdf) ...
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345 views

Do user level threads take advantage of multi processing?

I asked this question here on stackoverflow, but maybe because of off-topic over there, it didn't received proper response. Does user level threads take advantage of multiprocessing ? I read one such ...
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When was manual dynamic memory managment introduced?

Original Fortran only had static memory. Algol introduced stack allocation. Lisp had Garbage Collection. But when where manual dynamic memory management such as in C introduced. In C memory can be ...
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100 views

Processes running in Distributed Systems (Advanced Operating System)

I had a test today, there was a question that was a bit confusing. Anyway I am asking the question, from memory, and explaining what I answered. It would be great if someone could explain if I did ...
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409 views

Clock variant of the Second-Chance page-replacement Algorithm vs. standard Second-Chance Algorithm

A sample question for my upcoming Operating Systems exam is: Under which circumstances would the clock variant [of the second-chance algorithm] be preferred over the standard second-chance ...
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200 views

Solve a basic mutex lock problem while preventing deadlock

I am solving a problem with a bridge, where you have a one way bridge with people coming from each side. To solve this problem while preventing deadlock (two people going opposite directions on the ...
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1k views

want to know concept behing Multilevel paging

In order to use large size page table hierarchical paging is done . In case of two level page table scheme . for : logical address space - 32bit - $2^32$ page size - 4kb i.e $2^12$ It is mentioned ...
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5k views

Effective Acces time in Demand Paging system with Associative memory

Q: Consider a demand-paging system with a paging disk that has an average access and transfer time of 20 milliseconds. Addresses are translated through a page table in main memory, with an access time ...
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1answer
2k views

Does Second chance Page replacement algorithm suffer with Belady's anomaly?

In Second chance Page replacement algorithm(clock algorithm), if all the Reference bits are set to one, then the algorithm behaves just as FIFO. Considering this case, can we conclude that Second ...
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Does exec cause a context switch?

If we start a new process with exec('process-2') Does this cause an immediate context switch in order to halt the current process and then start the new '...
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20 views

What assumptions do I have to make about monitors (in OS)?

I am taking a course in Operating Systems. I am going through old exams and there is a question about monitors. We are supposed to give a solution for the producer-consumer problem using monitors. ...
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11 views

Does a safe state ensures there will never ever be a deadlock?

In Banker's algorithm of deadlock avoidance, if one can obtain a safe state, does that necessarily mean there will never be a deadlock, or is there still some way that the system could fall into a ...
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31 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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How many page-table entries can fit into TLB space

I am looking to calculate how many page-table entries can fit into a corresponding TLB space (Translation Look-aside Buffer ). I just want to make sure I am getting the calculation right, as I fear I ...
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12 views

How many page-table entries are needed in case the program uses the whole logical address space

Say I have: page size = 2^12 bytes physical memory = 2^24 bytes logical address space = 2^32 How many page-table entries are needed in case the program uses the whole logical address space?
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1answer
48 views

Converting physical address to logical

In 8-bit address space there are 16 pages and the page table stores: 68792EA51BD3CF04 (hex) The physical address is 39h, what is the corresponding logical address? I have literally no idea what to ...
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1answer
27 views

How many segments a process can have in operating system employing Segmentation for memory management

Some facts about "Segmented Paging" 1) Each process has one segment table. 2) There is one-page table per segment. Fact about "Paged segmentation" 3) Contains page table of segment table. Now ...
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14 views

Can many threads run in a parallel in many-to-one model?

The book I am reading suggests that in a many-to-one multi-threading model, the threads are unable to run in parallel in a multi-core system. I am thinking this is not the case because if we have many-...
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1answer
31 views

Calculation of speed up of a program executed in multi-threaded system

Speed up of execution of a program is to be calculated within a multi-threading rather than a single thread system. The program's 30% instruction can be executed serially & rest can be executed ...
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24 views

Which page replacement algorithm causes thrashing

This is rather simple conceptual question. I can guess the answer, but no text explicitly discuss thrashing in the context of different page replacement algorithm. So I want to take your confirmation ...
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45 views

What are necessity and sufficiency?

I was reading deadlock topic from Operating Systems book by Stallings. It states four pre requisites for deadlock: Mutual exclusion No preemption Hold and wait Circular wait It then have following ...
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1answer
78 views

How can I solve this deadlock related problem mathematically?

I came across following problem: A system has n resources R0,…,Rn-1,and k processes P0,….Pk-1.The implementation of the resource request logic of each process Pi is as follows: ...
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17 views

Why we need size of the page table should be some fraction of virtual address space

The Page Table should have all virtual page number which are in its logical address space, Why it's the case? Is it because we want to access Page Table entry fast just like an array where key is ...
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1k 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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28 views

Any good source explaining multiprocessor synchronization techniques and their implementation

I need to study how synchronization is done in a multiprocessor operating system, but I am unable to find a good source. I have read about it in the book "Modern Operating System" by Tanenbaum, but I ...
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16 views

Inputting values to register files

I'm trying to understand how to register files. The question below is from past exam paper: The following diagram shows the register-file from a simple 8-bit machine I don't fully get register ...
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34 views

How can an unstable kernel write a memory dump?

I always wondered how a kernel that became unstable, e.g. due to a BSOD or a kernel panic, is able to do specific tasks. For example, if a Windows driver corrupts the stack of the kernel. It leads to ...
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Understanding Bounded Waiting

I am trying to understand bounded waiting and i have a question. The definition is as follows: Bounded waiting - There exists a bound, or limit, on the number of times that other processes are ...
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296 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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346 views

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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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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28 views

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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36 views

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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63 views

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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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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27 views

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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975 views

CPU scheduling Algorithm SJF VS SRTF average waiting time?

Let's say we have two CPU scheduling algorithm as SJF and SRTF and we have a arbitrary pool/set of processes with different ARRIVAL TIME and CPU BURST, then what CPU scheduling algorithm will result ...
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Operating Systems - Why Stack Growths For a Fixed Parameter N Are Inconsistent?

I am taking an Operating Systems course and as a project, we are printing the content of the PCB of a process from task_struct of that process and its mm_struct & vm_area_struct pointers. During ...
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Segmented Paging mechanism virtual and physical pages

I have a system which uses segmented paging. Every address is divided as follows: (s,p,d) = 2,2,11. Main memory has a capacity of 32KB. There are 4 segments which have 4 virtual pages each. I have to ...
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49 views

EDF vs Rate Monotonic context changes

I'm studying real time scheduling algorithms. In particular EDF and Rate monotonic. I have an intuition that using EDF we have less context changes than using Rate Monotonic. But i dont know how to ...
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268 views

Logical to Physical Address

I have an exam coming up and my teacher posted a practice exam for it. Problem is that I solved the question but I am not sure if I am doing it right or getting the right answer as he refuses to give ...
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139 views

Utilization Factor, periodic tasks and schedulability

We have 2 periodic tasks that start at the same moment in a monocore processor. Why can happen that, even if the utilization factor is <= 1, the 2 periodic tasks are not schedulable ? For example, ...
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An energy consumption problem

We want to show one schedule of jobs consumes less energy than another one. For example, there are two schedules A and B. Both the schedules A and B schedule two jobs $j_1$ and $j_2$ with execution ...
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1answer
2k 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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126 views

Why TurnAround Time is considered as Performance Metric for Scheduling Algorithms?

I know what is turn around time but i am confused why wating time is not considred as Performance Metric for Scheduling Algorithms Since it gives the time for which a Process will wait till it gets ...
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68 views

What happens when accessing 0x00ABBA?

Given the following page table with a 24 Bit virtual address and 4KB page size and 4 byte long entries (%X means hexadecimal values): I don't understand how to translate e.g. address %X00ABBA here. I ...
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33 views

How operating system is generic with different processors?

I have one query, Operating system (In machine language) as I study is the combination of opcodes that executes, Now, the opcodes are dependent on the instruction set architecture like how and which ...
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649 views

How do you calculate when effective access time is greater than cache access time?

I'm having trouble understanding how to calculate effective access time, hit ratios and cache access times. I'm unfamiliar with the concepts and would love help, or an explanation on how to solve this ...