Questions tagged [operating-systems]

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

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16 views

Research papers related the Android OS's Adaptive Battery and Screen Brightness

I want to read the details of the Adaptive Battery Optimization and Adaptive Brightness techniques used in the Android operating systems as mentioned in this wired.co.uk article. I tried looking for ...
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16 views

External fragmentation of memory

Im trying to calculate the external fragmentation of a memory with the content UFFFUUFFUU where U is used, and F is free. Im confused as to how to do this, when i dont know the number that Used is ...
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How Are Segment Descriptors Used

I am following through James Molloy OS tutorials and I can't get my head around the GDT. I understand that it contains entries that describe segments, what I don't understand is,how are the segment ...
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3k 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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Doubt in effective memory access time in case of n level paging + TLB

I am getting confused with calculation of EEMAT(Effective memory access time). I decided to close the book and think on my own and make an equation. Please see whther this is correct or not. I thought ...
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44 views

how worst fit better than best fit?

I am a beginner. I have recently started studying OS. In textbook, it is written as best fit is worse than worst fit. Reason - external fragmentation. IMO,in case of variable partionioning, best ...
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327 views

What architectural features will allow this microprocessor to access a separate “I/O space”?

I'm studying for my final and don't understand this question. Here is the full question (from Stallings 8th edition): Consider a hypothetical microprocessor generating a 16-bit address (e.g., ...
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What is the average turnaround time?

For the following jobs: The average wait time would be using a FCFS algorithm: (6-6)+(7-2)+(11-5)+(17-5)+(14-1) -> 0+5+6+10+13 -> 34/5 = 7 (6.8) What would the average turnaround time be?
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doubt in pipelining

I am not from cse but trying to learn computer architecture on my own. Please clarify the following. In case of pipelining, each stage or subcomponent or subtask is assumed to be done in 1 CPU ...
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36 views

When does a semaphore issue a wait and when does it issue a signal?

In my textbook, Operating Systems: Internals and Design Principles (9th Edition) by William Stallings in chapter 5, it explains how semaphores work: The fundamental principle is this: Two or more ...
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Study of cache behaviour of algorithms on Virtualbox

I want to study certain cache oblivious algorithms and cache behaviour of some other algorithms I wrote in general. I want to understand, is it advisable, if I do this study in an virtualized ...
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1answer
23 views

Paging - access less than a page of memory

I'm having a bit of trouble understanding how less than a page of memory can be used. From what I understand, memory is given out in page size chunks - say pages are 4096 bytes, and 4 bytes are ...
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Are there any models of operating systems which don't require rings of privileges, that are also secure?

I am working on a simple operating system in JavaScript and have noticed that there are two kinds of processes: the "main" process (or "kernel" process), and all the other processes. Basically they ...
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1answer
172 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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1answer
44 views

Can timestamp be used in synchronization of processes having Race Condition?

I am wondering whether timestamp can be used to solve process synchronization problem, when race condition occurs? Below is an algorithm for entry as well as exit sections for every process who wants ...
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48 views

Given only TLB Lookup time, and memory access time, can the TLB hit rate be negative?

I'm given the following problem: TLB lookup time is given as 8ns and memory access time for a computer system is given as 40ns. What should be the TLB miss rate to achieve effective memory ...
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10 views

What IaaS services are needed in order to run a server?

I have just learn't about Iaas, Paas and Saas and I was wondering whether a business can host a server by using IaaS services. However, many IaaS providers such as AWS, Azure and Google provide ...
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51 views

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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2answers
9k 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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1answer
66 views

Why no context switch is required in case of spinlock in operating systems?

I have a query regarding the fact that how Spinlocks are advantageous in terms of context switching ?
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70 views

What is the name of this experimental OS?

I am trying to find an OS that had a network to verify it's users. It classified itself in classes going from greatest signifigance to least, and the names were galaxy, system, planet, comet etc. I ...
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2answers
6k views

What is a GPU year?

I am reading papers in machine learning and they say things like, "This computation took $x$ number of GPU years". What is a GPU year? How long is that?
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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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2answers
2k views

Does a context switch happen when a process has terminated?

I know this might sound like a newbie question but let's say we have a priority based scheduling algorithm (non-preemptive) where all processes arrive at time 0 and based on priority the order is P1, ...
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1answer
111 views

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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1answer
83 views

How can a 32bit CPU have an addressable memory size of 16TB?

Frequently, on a 32-bit CPU, each page-table entry is 4 bytes long, but that size can vary as well. A 32-bit entry can point to one of $2^{32}$ physical page frames. If frame size is 4 KB (212), ...
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47 views

Expected value of next CPU burst using exponential averaging

The burst time is needed for Shortest Job First (SJF) and Shortest Run Time First (SRTF) scheduling. To get the approximate burst time, we use the equation $$\tau_{n + 1} = t_n + (1 - \alpha)\tau_n$$ ...
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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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64 views

Lack of Stack Pointer Register

Suppose a processor lacks STACK Pointer Register. But, It does have STACK. Then, in my opinion, a program will still be able to call subroutines but, will be unable to return back from the subroutines....
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2k views

Scheduling algorithms and quantum time

I would like to know what impacts does a scheduling algorithm, let's say Round Robin or FIFO, have on an Operating System. I understand that a scheduling algorithm has the processes run in burst then ...
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1answer
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Writing a multitasking operating system for a processor without MMU

I've been thinking of writing a hobby operating system for some of the ARM processors. There are many popular single-board computers with ARM MPU, so I simply wanted to purchase one of those (choosing ...
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65 views

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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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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262 views

What is a batch based interface? [closed]

I came across this description of Batch Interface: "commands and directives are used to manage those commands that are entered into files and those files get executed. " I would really appreciate if ...
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31 views

Doubts on Virtually Indexed,Physically tagged Cache

I tried referring a few material (videos on youtube and this link as well), but I still couldn't wrap my head around the concept. My (brief) understanding of the Virtually addressed, Physically ...
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1answer
97 views

How are hardware interrupts handled?

I have read that a hardware interrupt is handled asynchronously by the CPU, which means that the interrupt signal may arrive at any point of time with respect to the CPU clock cycle. Now, this means ...
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1answer
49 views

Software management of TLB misses?

I'm reading an OS textbook and it was talking about TLB misses being handled by software. I'm very new to all this by the way. So there's a context switch to some kernel procedure. But surely in this ...
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1answer
141 views

What is a 'dynamic entity' in computer science?

I am doing some reading into computer science and how the computing system works in order to be ready for my 1st year at university doing a Computer Science degree. I came across a term within the ...
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1k views

Segmentation and paging

I am given a system with a segmented paging architecture. Both physical and virtual address spaces contain $2^{16}$ bytes each. The virtual address space is divided in $8$ equal size segments. The ...
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23 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
3k views

What is the difference between caching, buffering and paging? Expecting a detailed answer on the OS level

I have been reading about caching and buffering it seems about the same to me can't get hold of the differences clearly and paging, for now the only difference I understand between paging and caching ...
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1answer
45 views

How are logical addresses of instruction operands mapped to physical addresses?

Is address translation for all operands in single instruction done only once and then are all operands fetched continuously? For example, consider any dummy instruction ...
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94 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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49 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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23 views

Comparing wait-signal alternatives for synchronizing two piece of programs

I came across following problem: A certain computation generates two arrays a and b such that ...
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1answer
61 views

Designing solution to critical section problem with two semaphores vs single semaphore

I came across following problem: Let two processes P1 and P2 are there: ...
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1answer
1k views

How do stack-based cache algorithms avoid Belady's anomaly?

I was going through page replacement algorithms from Galvin's Operating System book. I encountered this line about LRU: A stack algorithm is one in which the pages kept in memory for a frame set ...
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24 views

Does this state certify to be called as a deadlock?

I came across following problem: Barrier is a synchronization construct where a set of processes synchronizes globally i.e., each process in the set arrives at the barrier and waits for all others ...
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1answer
84 views

How does dynamic memory-allocation exactly work?

I have wondered about ordinary code. Assume we are running this code on any modern System like Unix/Linux/Mac/Windows. This code is C, but it should work with every language which is close to the ...
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1answer
81 views

Why is 2^32 in a 32-bit system = 4GiB and not 4Gib?

I was watching this video 32-Bit vs 64-Bit - The Advantage and at 1:19 (timestamp) the narrator mentioned the 4GB memory allocation for the 32-bit system. I later found out it should've been 4GiB but ...

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