Questions about how operating systems decide which process to execute at which time.

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Round-Robin Scheduler - What exactly is the quantum time used for?

Suppose you have three stages for a job: Creation stage = the job gets created Executing stage = the job is executed/served Finishing stage = the job is "marked" as finished. Now, say the quantum ...
2
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1answer
22 views

How are system calls handled in a virtual machine?

Quoting wikipedia, a system call is: In computing, a system call is how a program requests a service from an operating system's kernel. This may include hardware related services (e.g. ...
8
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2answers
24 views

What guarantees do “soft” real-time operating systems actually provide

I think I know what a "hard" real-time operating system is. It is an operating system with a scheduler that provides a contract with the application programmer. An application provides a deadline ...
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1answer
23 views

Which process states exist a multi-processor machine?

In a single-processor architecture, A process might be New, Ready, Running, Blocked and Terminated. Are there any additional states in a multi-processor architecture?
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1answer
47 views

Does a multi cpu system not improve the first come first serve (fcfs) cpu scheduling algorithm?

I created a program that simulates the fcfs scheduling algorithm. First I implemented it for a single core, then modified it for four homogenoues cpus. I compared the results with several datasets, ...
2
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1answer
91 views

How does the OS know the physical address of a process' first memory page?

If I have a program, its instructions are stored on the hard drive. When I double-click the executable the pages of memory for this process must get loaded in to RAM. However, for the pages to get ...
2
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0answers
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How can I talk about priority inversion if it's impossible to specify priority?

In the paper: Leslie Lamport: What It Means for a Concurrent Program to Satisfy a Specification: Why No One Has Specified Priority; ACM Symp Principles of Programming Languages, (POPL-12):78-83, ...
0
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1answer
62 views

How to build/recognise a deadlock-free order of resources

I have been faced with a problem where three concurrent processes X, Y ,Z execute three different code segments that access and update certain shared variables. Before entering the respective code ...
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1answer
301 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. ...
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1answer
243 views

What happens when time slices are too short or too long?

What bad things can occur when the lengths of the time slices in a multitasking system are too small? What can happen when they are too big? How should the length of the time slice be chosen?
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1answer
69 views

processes response time confusion

An OS contains 10 identical processes that were initiated at the same time.Each process contains 15 identical requests. Each request consume 20 msec of CPU time.A request is followed by an I/O ...
2
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1answer
218 views

A variant of job assignment (scheduling) problem with variable time span

The problem is a scheduling problem with n jobs and k machines. Each job i can be started at any time, but its duration is not exactly known except a time span interval. For example, a job may take ...
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2answers
978 views

Disk scheduling and process scheduling

Whats the diffrence between Disk scheduling and process scheduling? I mean i know the roles of disks and processes, but it seems to me they both have the same aim. to reduce monopolies, they even both ...
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2answers
5k views

The convoy effect in process scheduling

As I understand the convoy effect, in the context of vehicular traffic in a road system. A slow moving group of vehicles passes through the system, slowing traffic even in areas which were not ...
7
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3answers
10k views

What is the difference between Multiprogramming and Multitasking

I am finding it difficult to clearly differentiate between Multiprogramming and Multitasking. My primary source has been Wikipedia, but the WP article seems to be a little at odds with some less ...
2
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2answers
226 views

What mechanisms prevent a process from taking over the processor forever?

Suppose a process keeps running code (e.g. an infinite loop). How can other programs take over? What prevents the process from remaining active forever?
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1answer
110 views

Process state in multi threaded process

What would be the process state in a multi threaded process, in which threads are in different states (running, waiting, blocked etc)
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1answer
473 views

Scheduling algorithms and quantum time

I would like to know what impacts does a scheduling algorithm say Round Robin of FIFO have on a Operating system. I understand the a scheduling algorithm has the processes run in burst then switch ...
4
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1answer
792 views

First-Come-First-Serve scheduling algorithm - what happens to process after returning from I/O? where does it go in the queue [closed]

There are three processes in line, $P_0$, $P_1$ and $P_2$. $P_0$ registered and executes $P_0$ I/O blocked so $P_1$ executes $P_1$ I/O blocked $P_0$ executes. ?? After $P_1$ must come $P_2$ that ...
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1answer
578 views

How are threads implemented in different OSs?

I was reading Linux Kernel Development by Robert Love, where I came across this Linux takes an interesting approach to thread support: It does not differentiate between threads and normal ...
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4answers
2k views

What is meant by interrupts in the context of operating systems?

I've decided to read Operating Systems Concepts by Silberschatz, Galvin Gagne (8th edition) over the summer. I've gotten to a topic that's confusing me - interrupts and their role as it relates to ...
4
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2answers
11k views

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?
4
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1answer
2k 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 ...
9
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2answers
546 views

Round-robin scheduling: allow listing a process multiple times?

In a round-robin scheduler, adding a process multiple times to the process list is a cheap way to give it higher priority. I wonder how practical an approach this might be. What benefit does it have ...
8
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1answer
351 views

Are two-level schedulers only useful to manage swapping?

Two-level scheduling is useful when a system is running more processes than fit in RAM: a lower-level scheduler switches between resident processes, and a higher-level scheduler swaps groups of ...
14
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4answers
720 views

Does cooperative scheduling suspend processes when they perform an I/O operation?

Many operating systems references say that with cooperative (as opposed to preemptive) multitasking, a process keeps the CPU until it explicitly voluntarily suspends itself. If a running process ...