Questions tagged [operating-systems]

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

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How can a CPU access more memory locations than 2^wordsize?

I noticed that CPU's like the 8086 and especially the 8080 have the ability to access more memory than what one would normally assume. The 8080, for example, has an 8-bit word size but can use a 16-...
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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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2answers
123 views

Why operating system needs interrupt stack, if it has process control block?

I'm reading about an operating system but some concept confuses me. What doesn't confuse me: When an interrupt or system call or processor exception occurs, it happens when user mode tries to ...
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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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1answer
124 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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1answer
68 views

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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0answers
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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1answer
195 views

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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1answer
128 views

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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0answers
514 views

Latency and Throughput Bounds

Say that I have a superscalar processor and I am given the latency, issue and capacity (in clock cycles) for different instructions. What is the general formula for latency bound and throughput bound?...
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22 views

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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1answer
45 views

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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1answer
831 views

Deadlock and safe state

I read that system being in safe state doesn't guarantee that deadlock is not possible. Can someone give me an example where system is in safe state and deadlock is possible?
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1answer
64 views

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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1answer
33 views

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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1answer
48 views

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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1answer
7k views

How does the OS determine the CPU burst time of a process?

This question is related to OS. After having solved many problems in CPU scheduling I was wondering how does the CPU know the burst time of all the processes in the main memory before executing them? ...
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4answers
2k views

Operating System - CPU scheduling Decisions

I understand that CPU scheduling takes place on 4 circumstances listed below: When the process changes state from Running to Ready Changes state from Running to Waiting Changes state from Waiting to ...
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3answers
6k views

Look Ahead buffer vs Translation Look aside buffer

I know that Translation look aside buffer is used for address translation in paging to achieve better performance. I came across term called Look Ahead buffer in a document which said it implements ...
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1answer
99 views

What does 'buffering' mean?

I read the lecture 4 of CS162 (UC Berkeley: https://inst.eecs.berkeley.edu/~cs162/sp17/static/lectures/4.pdf), but I got little bit confused about the meaning of the keyword "buffered" they used when ...
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0answers
294 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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0answers
22 views

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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1answer
2k views

User level threads are transparent to the kernel?

Find whether given statement True or False? Explain. User level threads are transparent to the kernel? My attempt : False. Since, user level threads are managed by a user level library however, ...
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0answers
135 views

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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1answer
179 views

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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0answers
335 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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1answer
32 views

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 ...
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1answer
69 views

What does it mean " The outer level page table need not be page aligned?

The question is in context to multilevel page table. I was trying to solve numerical on multi-level paging and noticed that page size might not be same at all levels. I came across the point "Outer ...
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0answers
752 views

Difference between Response time, Execution time, and CPU time

I studied Computer Architecture from David A. Patterson and have came across the idea of Response time. Response time also called Execution time. The total time required for the computer to ...
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4answers
40k views

What threads share in general?

Well this is general question. And if anyone want to make it implementation specific then I will prefer Unix related stuff. But first need to know following problems in generality: I read single ...
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1answer
34 views

Why is there no one to many Multithreading Model?

I am studying various multi-threading models. Here the user threads are mapped to Kernel Threads. They are - ...
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1answer
15 views

multithreading - duration of jobs

" How long will it take for 2 jobs to complete if they're running in parallel, knowing that both have a total of 20 minutes of CPU usage time and 50% IO" I calculated the CPU usage: ...
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0answers
12 views

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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1answer
32 views

Threads and Operating System

In a computer, the processor executes different threads and changes between them, the operating system is a program at the end that it´s being executed by the processor, there exists the posibility ...
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0answers
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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1answer
470 views

How can context switch affect the modification of a variable?

float myTotalAmount=0; void update(float amt){ myTotalAmount+= amt; } Task A called update(10); Calculated ...
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1answer
70 views

Round-Robin fashion exercise

In my Operating Systems class I have an exercise to sketch out how a round-robin algorithm would apply to a specific scenario, which is the following: Now the correction that I was provided with by ...
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2answers
222 views

Characterize an OS as multiprogrammed OS

Which of the following features will characterize an OS as multiprogrammed OS? More than one program may be loaded into main memory at the same time. If a program waits for certain event another ...
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0answers
29 views

Definition of multiprogramming [duplicate]

Which combination of the following features will suffice to characterize an OS as a multi-programmed OS? a. More than one program may be loaded into main memory at the same time for execution b. If ...
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0answers
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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1answer
51 views

ARM STM instruction: page fault problem with MMIO

The ARM STM instruction is described here in the ARM manual. This instruction writes all or a subset of registers at memory locations starting from a base memory ...
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1answer
40 views

Instructing operating system - Knowing it's functionalities

TL;DR: I would like to know how a programming language, the OS and drivers work together to perform a task. I (and we all) have used various softwares/modules/packages on the top of our OS which ...
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2answers
703 views

Increment and Decrement on binary semaphores when their values are $1$ and $0$ respectively?

What happens if we increment binary semaphore $x$ when it is equal to $1$. E.g A process executes $V(x)$ when $x==1$; What are the possible cases then- Process would be blocked till $x$ becomes $0$. ...
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6answers
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Does Deadlock imply Starvation

If there is a deadlock between the processes does that mean that there is starvation also? My Thinking: deadlock is no process using that resources , but starvation is like not giving chance to only ...
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1answer
34 views

Is OS mode required for accessing general purpose registers

In which of the following cases a process executing in user model is required to enter into the OS mode? (a) Decreasing the value of unsigned integer value in a register to less than 0 (b) Accessing ...
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2answers
33 views

Who decides that process needs cpu time or not?

I wonder how does particular process gets CPU time or resources whenever it's required to execute some instructions? When a process is in the idle state or waiting for input, it's not occupying the ...
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1answer
3k views

What is the real advantage of Google's new Fuchsia operating system kernel?

Google's new in-production OS which it desires to replace not only Android but many other devices utilizes a completely new kernel: The code differs from Android and Chrome OS due to its being ...
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0answers
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'...