Questions tagged [operating-systems]

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

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How can i draw a general resource graph which cannot be completely reduced but which is free from deadlock?

How can i draw a general resource graph which cannot be completely reduced but which is free from deadlock? A general resource graph which can be completely reduced and hence is free from deadlock is ...
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Default scan order in SCAN and LOOK disk scheduling algorithms

I've been learning various disk scheduling algorithms in Operating systems. I wanted to know if there was any default scan order in SCAN, C-SCAN, LOOK and C-LOOK algorithms, like towards higher ...
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Resource Allocation Graph Algorithm

In the book Operating System Concepts, it is said that: A claim edge $P_i \rightarrow R_j$ indicates that process $P_i$ may request resource $R_j$ at some time in the future. [emphasis added] ...
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470 views

Physically indexed virtually tagged cache

PIVT cache is indexed physically so address translation using TLB is needed to get into cache and we use virtual address as the tag for comparison . I read that homonym is a problem which is caused ...
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Internal fragmentation basic concept

Suppose I have two processes of 50 bytes and have only one partition (hole) of 100 bytes. Suppose the first process takes up the partition and 50 bytes is remaining . Can the second process reside in ...
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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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372 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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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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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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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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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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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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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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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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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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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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Does Dekkers solutions to critical section problem ensure progress?

I was reading concurrency control section from Operating Systems book by William Stallings. In this book, he gives three attempts by Dekker to give solution to critical section problem: Attempt 1 <...
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What does this mean: “The compile-time and load-time address-binding methods generate identical logical and physical addresses”?

I read this in my Operating System textbook. Does it mean that the logical addresses generated by compile-time binding scheme are the same as the logical addresses generated by load-time binding? Or ...
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Is this a deadlock?

Consider we have two processes P1 and P2. There are also two semaphores M and N which are initialized to zero. Here's how they execute: ...
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Deadlock: can the processes know about deadlock occurrence

Deadlock can happen when two processes are waiting for resources held by each other. Here can the two processes know that they are waiting for each other to release resources?
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Deadlock in resource allocation graph

I am unsure if there is a deadlock in this particular graph. Not sure if P2 and R2 make a cycle. As well as P2 - R3 - P1 - R1 - P2. It seems there is a cycle, but not sure if there is a deadlock ...
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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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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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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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35 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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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378 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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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'...