Questions tagged [operating-systems]

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

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1answer
31 views

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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4answers
9k views

Calculation of effective average instruction execution time in a 2-level paging system

System has a two level paging scheme Average CPU time for a instruction = 100ns Average number of memory accesses per instruction = 2 Regular memory access = 150 ns Page fault service time = ...
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1answer
3k views

Bounded waiting and progress requirements of critical section problem solution based on exchange instruction

Atomic exchange instruction is given as follows: void exchange (int *a, int *b) { int temp; temp = *b; *b = *a; *a = temp; } Now consider the ...
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1answer
344 views

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 ...
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1answer
425 views

Can a safe state in Banker's Algorithm cause deadlock eventually?

I know that unsafe state does not always mean deadlock. That is a situation that banker's algorithm does not detect deadlock accurately. I am just wondering if there is any example of a safe state ...
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1answer
47 views

Fork() execution and number of processes

If a process executes the following code fork(); fork(); fork(); The total number of child processes created is given as 7 by a text book. But how does that ...
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3answers
9k views

Exponential averaging for SJF CPU scheduling

Calculate the exponential averaging with $T_1 = 10$, $\alpha=0.5$ and the algorithm is SJF with previous runs as $8,7,4,16$. 9 8 7.5 None I am getting 4. None as the answer. But ...
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2answers
8k views

Which queue does the long-term scheduler maintain?

There are different queues of processes (in an operating system): Job Queue: Each new process goes into the job queue. Processes in the job queue reside on mass storage and await the allocation of ...
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1answer
763 views

Processor pipelining question: number of instructions per second

A question from the textbook Modern Operating Systems by A. S. Tanenbaum reads as follows: A computer has a pipeline with four stages. Each stage takes the same time to do its work, namely, 1 nsec. ...
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1answer
287 views

Are multiple interrupts generated when I hold down a key on my keyboard?

When I hold down a key on my keyboard, a continuous stream of characters is generated and is displayed on the text editor, Now since pressing a key is a hardware interrupt, so does holding down a key ...
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0answers
32 views

Software and hardware communications [closed]

When you install an OS on a piece of hardware such as a Macbook, what is happening logically? In other words, how does the software "talk" to the hardware? Is it the same logical process with every OS ...
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2answers
2k views

Algorithm for wait-for graph

During the process of deadlock detection, the wait-for graph can be obtained from the resource-allocation graph. To detect whether there is a deadlock using the wait-for graph, can topological sort be ...
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1answer
39 views

What is the mathematical principle of buddy algorithm?

The buddy algorithm is: The buddy for any block of size $2^k$ is another block of the same size, and with the same page frame number except that the kth bit is ...
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3answers
3k views

Virtual Address and Physical Address Space

A machine has 48-bit virtual addresses and 32-bit physical addresses. Pages are 8K. How many entries are needed for a conventional page table ? The answer is 2^35 entries Why not (2^32) / (2^13) = ...
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1answer
922 views

What's the difference between user registers and kernel registers?

I am reading Operating Systems: Three Easy Pieces, but I can't fully understand the following paragraph. It's from the 6th chapter of the book. I think it's self-contained, so I quote here. Note ...
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0answers
162 views

How is context switching disabled in a process?

By what provision is context switching disabled in a process ? Or is it the case that if a process is in in kernel mode , context switching is disabled by default ?
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OS process management

Assume a process execution interrupted at the middle and CPU started executing a different process.How does the OS handle this situation?
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1answer
92 views

What are the recents topics of research that combine both systems research and theoretical computer science?

I am an undergraduate majoring in Computer Science and Mathematics. For my undergraduate research, I would like to work on something that lies in the overlap between systems research and theoretical ...
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1answer
77 views

why do we run out of heap space even if we have virtual memory?

Whenever we try to get space in heap(using malloc or new) we can get out of heap space error if it exceeds the limit. But, we have virtual memory so why can't OS allocate that much space and then do ...
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1answer
892 views

Peterson Algorithm for process synchronisation

Consider Peterson's algorithm for mutual exclusion between two concurrent processes i and j. The program executed by process is shown below. repeat ...
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1answer
747 views

What is hardware trap?

Since it's called a trap I consider it caused by software, so why it's called a hardware trap? And how does it work?
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0answers
20 views

Operating System: Redundancy of implement a monitor using semaphores in my textbook?

Why the part highlighted the following picture is need? I've been trying to follow to logic flow of it as follow: Imaging a Situation: Two processes enter/call F, first A, second B: Process A: <...
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0answers
231 views

Operating System: Busy waiting is not eliminated with semaphore?

Why the busy waiting is not eliminated even after we put the current process into the process list and "block()"ed it? So even if the process is in waiting state we still call it "busy waiting"? I'm ...
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1answer
199 views

Operating System: About user thread and kernel thread?

Is that a "thread" consists of both "user thread" and "kernel thread" as two parts? And when I create a "thread", is that I create a "user thread" and another "kernel thread" is created "in the ...
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1answer
374 views

How do modern Operating Systems detect process starvation?

So first off do the modern operating systems like windows and linux have a method for detecting starvation? if not, why? and if they do, then how are they going to detect starvation of a process? (...
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1answer
75 views

Operating System: replace the process's memory space with a new program

What does it mean that "replace the process's memory space with a new program"? So who's memory space will be replaced by whom?
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0answers
29 views

Why isn't a process's PCB present in its memory?

I checked wikipedia PCB and its written that - Since PCB contains the critical information for the process, it must be kept in an area of memory protected from normal user access. In some operating ...
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2answers
93 views

How is space from malloc allocated?

Whenever we load a process (which consists of object code, static and global variables, stack and heap space) into main memory it would be of fixed size. But, the program doesn't know in advance how ...
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3answers
178 views

Is it 100% OK to say “All software doesn't need to know the system lower than the architecture level”?

Most of you know this diagram. If this diagram is true, all software is free to not know the levels lower than ISA. But it's not true. Softwares like performance-critical programs or system softwares ...
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1answer
36 views

Linux OS/HW VM cooperation

From what i've learned, the HW is responsible for setting the accessed and dirty bits in the PTE of a process, and the OS is responsible for turning them off. My question is why? The first part, i ...
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1answer
103 views

What is the benefit of using one to one thread mapping model instead of Many to Many or two level?

So in the silberschatz O.S book it says Windows uses one to one model (mapping user level threads to kernel level threads) but why? i thought many to many and two level models are much better, ...
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1answer
808 views

What is the relation between Time Sharing operating systems and Round Robin CPU scheduler?

So i have asked this before, but i still didn't get my answer so I'll try to make my question more clear this time : Based on my O.S book, Time sharing operating systems switch between processes ...
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1answer
1k views

How does the TLB identify a particular process?

I have read that the translation lookaside buffer (TLB) is implemented in hardware and stores the page numbers and the corresponding frame numbers for faster lookups. Now suppose there are two ...
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1k 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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1answer
169 views

NX Bit in x86 vs x86_64

I've been reading about how the kernel manages memory in x86 from this popular blog post(https://manybutfinite.com/post/how-the-kernel-manages-your-memory/) and had a few questions. There is a part ...
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2answers
4k views

What's the difference between Process Context and Process Control Block?

I know that Process Context is something that is stored when a process is preempted, containing all the necessary info to restart the process at a later time. I also know that the Process Control ...
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1answer
33 views

How can segment be 60KB

I read that each segment is 64KB,but how? If you have address ABCD:EFGH , then 1 segment is 16B if it is addreses by bytes. How do they don't overlap? Example: 0000:0010 = 00010 0001:0000 = 00010 , ...
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635 views

Definitions of: virtual address space, page size

(I can't seem to find actual definitions of these terms anywhere, only hints and guesses). Is it fair to say, that: Virtual address space is the amount of bytes that can fit into RAM cells of all ...
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1answer
81 views

Multi-processing cpu utilization estimate

I find a formula on my book to estimate cpu utilization under multi-processing. $ U = 1 - P^n $ U: cpu utilization P: cpu idle I want to know why or how to proof. Edit: The book is about ...
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1answer
111 views

I have a question about resource alocation to avoid dead lock

In the code below, three processes are competing for six resources labeled A to F.How can I modify the get request in each procedure in this graph to avoid dead lock You cannot move requests ...
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2answers
1k views

Since physical memory is the RAM where is logical memory stored on the computer?

Since logical memory maps to the RAM (physical memory) it has be stored somewhere right and it will obviously take large bunch of memory of itself. Where is it stored?
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22 views

Are process-safe mutexes shared between OSes?

I understand you can use process wide mutexes, but does this still apply if you have an additional virtualized operating system provisioned? For example, take two OSes: ...
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2answers
535 views

Hierarchical Paging memory requirements

OS Book written by Galvin et all states that if page size is 4KB and size of virtual space is 32 bits then 2^(32-12) page entries would be required which is too huge to store in memory!! Therefore ...
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1answer
2k views

How does an Operating System without kernel mode work?

Andrew S. Tanenbaum, in his book Modern Operating Systems (3rd Edition), states that the distinction between operating system software and normal (user mode) software can sometimes be blurred in ...
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1answer
5k views

Program compilation and execution flow

I was studying operating system concepts from Silberschatz, Galvin and Gagne's book (sixth edition) and I have some questions about the flow of execution of a program. A figure explains the processing ...
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1answer
19 views

Where are file-information like “created” or “last edited” actually stored?

I can access some information about the files ("created" or "last edited") on my PC. But where are those information actually stored? Are they stored by the operation system? Could be possible as if ...
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1answer
49 views

What is the meaning of idiosyncratic when refering to multiprocess abstractions?

I am currently reading this paper on library operating systems, more specific on Graphene. I stumbled over the following sentence: "Because multiprocess abstractions, such as signals or System V IPC, ...
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2answers
28k views

Size of address spaces (logical and physical)

Suppose a system in which addresses (physical and logical) occupy 32 bits, page size is 1024 bytes (210), and physical memory is of size 32MB. How many frames are in physical memory? Is the logical ...
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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 ...