# Questions tagged [operating-systems]

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

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### 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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### 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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### 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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### 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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### Dual boot from two separate physical storage devices [migrated]

I have a new laptop that has a 256GB NVMe SSD drive with Windows 10 currently installed. The laptop has 2 NVMe SSD slots, so I plan to move the 256GB SSD to the second slot, and insert a new 1TB SSD ...
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### Have to restart printer spooling evertime I prrint [migrated]

Okay, I sincerely apologize if this is the incorrect area to be asking this question, but I've searched high and low on the stackexchange lists for an area that best suits this topic. This area seems ...
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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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### Why does paging not have external fragmentation?

I have read that paging does not suffer from external fragmentation as the frames and the pages are all of the equal sizes, but when we store a last level page table in a frame at that time it may not ...
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### 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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### Why in the Map Reduce Implementation, why not stream the records to the reducer (via TCP) as they are being produced by the mappers?

In the Map-Reduce implementation, the reducers start when all mappers finish their jobs. Why don't we stream the records from mappers to reducers while they are being processed instead? I think there ...
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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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### 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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### How exactly does a CPU do process scheduling?

I know in theory how various scheduling algorithms work, such as round robin, where each process is given small time slices to run a few instructions, before the operating system passes execution onto ...
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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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### Why do OS and DBMS have their own synchronisation mechanisms, when OS can alone do it and it sits at the bottom of DB?

I know that synchronization is important in the OS, but why do we need a separate topic synchronization and concurrency in the DBMS? The OS concentrates on program synchronization while the DBMS ...
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### Single processor system supporting two running processes, A and B, with the following sequential execution patterns [closed]

Can anyone please help me with the following question? Consider a single processor system supporting two running processes, A and B, with the following sequential execution patterns: A: [CPU 8 ms; ...
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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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### what is the difference between Operating system and Window Systems?

Quoting from Tannenbaum_Operating_Systems_Design : On top of the operating system is the rest of the system software. Here we find the command interpreter (shell), window systems, compilers, ...
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### How does operating system display decimal numbers which are stored as binary? [duplicate]

What kind of magic happen with bytes in memory?
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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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### 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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### 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 ...