Questions tagged [operating-systems]

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

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An energy consumption problem

We want to show one schedule of jobs consumes less energy than another one. For example, there are two schedules A and B. Both the schedules A and B schedule two jobs $j_1$ and $j_2$ with execution ...
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177 views

How to Identify which instructions are represented by this microcode

I'm having issues with a question how to identify which instruction are represented by this microcode. The pc starts at 5000 and 7000 and 7001 have values 31 and 64 - I'm really confused how to ...
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File systems and writing one

I am going through the following series of lectures on OS development . http://www.brokenthorn.com/Resources/ In the fourth tutorial , I came across the term " OEM" parameter block that stores the ...
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1answer
91 views

How does a buffer overrun corrupt the return address?

I got stuck on the following note while reading a paper about computer security: The stack mixes program data and control data – by overrunning buffers on the stack we can corrupt the return ...
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529 views

What does an “I/O Task” mean?

While reading an article, I noticed the use of term 'I/O Task': Indeed, suppose the currently running process is performing an I/O task (which, by definition, does not need the CPU to be ...
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55 views

How does the OS detect B&B violation from hardware?

After reading about Base & Bounds memory protection mechanism from Stanford CS140 lecture notes, I understood from the explanation below that there is an ...
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1answer
3k views

What does 'relocation' mean?

I am reading about Base & Bounds memory protection mechanism, and I noticed the use of the term 'relocation' in the context of ...
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1answer
302 views

Does starvation freedom imply progress?

The above answer taken from the book https://www.amazon.com/Operating-Systems-Sibsankar-Haldar/dp/8131730220 says starvation freedom may not imply progress as processes can be deadlocked. I think ...
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Does MMU contain and manage CPU caches?

I read about Virtual Memory in various CS references, however I'm still not sure whether CPU caches such as TLB, L1 and L2 are ...
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929 views

The meaning of 'Pool' in Computer Science

While reading about SIMD on Wikipedia, I noticed the use of the technical term Pool in the figure below: I didn't know what it ...
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1answer
338 views

Determine deadline for periodic task that enter ready queue in RTOS

I am currently trying to optimise the scheduler of FreeRTOS and in general Real-Time Operating Systems as a Project. In FreeRTOS, and I suspect other RTOS as well, we don't specify the deadline for ...
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What does “map” mean?

I have encountered the term many times, in various CS education materials: L2 CS162 (UC Berkeley): Memory-mapped I/O L4 CS162 (UC Berkeley): Memory mapped files L24 CS61 (UC Berkeley): “...
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96 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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Deadlock necessary conditions [duplicate]

I read that the 4 conditions for deadlock prevention are necessary conditions and not sufficient. The four necessary conditions are :- Mutual exclusion. Hold and wait. No preemption. Circular wait. ...
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2k views

Operating Systems - SJN/Round Robin - turn around time + waiting time

2.(10 pts) a) You are given 4 processes in a batch system that all arrive at time 0 with the following CPU burst times: P1 : 35, P2: 25, P3: 13, P4: 22. Assuming there is no context switch ...
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7k views

Explain Hashed page tables in operating system

I have a difficult time understanding hashed page tables used in virtual memory management. Here is picture of the slide that I am referring to: I understand that p is hashed and then the hash is ...
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1answer
97 views

hardware interrupts and context switch

I have recently studied about interrupts and context switch i have read that the hardware interrupts cause the interrupt service subroutine to execute for this i read mixed articles saying that there ...
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1answer
428 views

Virtual Memory - Non-contiguous Memory Allocation

I'm studying for my operating systems final, and one question that my professor asked that I can't seem to find the answer to is the following: "Why does virtual memory use non-contiguous memory ...
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1answer
69 views

Existence of Real-Time Multiprocessor Schedule

Does an algorithm exist to check for the existence of a Real-Time Multiprocessor Schedule for aperiodic hard tasks(all of which have the same Release time)? Assumptions: The processors are Uniform ...
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44 views

Can you read a file as a binary number?

This is a pretty naive question, but I would like to better understand the basics of information storage on a computer. I am not concerned with the detail of how any one operating system achieves ...
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307 views

Difference between inverted page table and a standard one?

I know that for standard page tables each process would have its own page table and for inverted the OS would have it. But other than this what are the main differences between a standard page table ...
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1answer
351 views

Effectiveness of TLB

This is a book question: Suppose that a machine has 48-bit virtual addresses and 32-bit physical addresses. Suppose this same system has a TLB (Translation Lookaside Buffer) with 32 ...
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127 views

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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2answers
189 views

Why are programs executed in main memory?

Why are programs kept in main memory for execution? As per my understanding, we need a memory management scheme to manage several processes in the main memory. These things can be done in secondary ...
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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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1answer
472 views

External fragmentation in fixed size partitioning

Can external fragmentation occur in fixed size partitioning ? I searched everywhere but couldn't find a sentence which says external fragmentation is not possible in fixed size partitioning. Please ...
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1answer
537 views

Does interrupt (for I/O and etc) requires support of Preemption? What is the relation between interrupts and Preemption in O.S?

So i just don't understand the relation between interrupts and Preemption in O.S? For example in Multi-programming, do we need the support of Preemption or not? when a process needs I/O and sends an ...
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Do system calls always means a context switch?

When a system call takes place some kernel code must be executed. If some kernel code is being executed it means it can alter register values. So before this code gets executed the old process state ...
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3answers
448 views

How can a spinlock progress when it's busy-waiting?

I read that in spinlock, process keeps on waiting for the lock continuously in a loop until it receives signal(lock) or ...
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1answer
140 views

Are Test and set primitives as powerful as semaphores?

I get confused because i don't know if it is possible to use Test and Set primitives in case where more then one process can be enter in critical section at the same time.
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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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1answer
674 views

Signed and Unsigned Loads in a 32-bit Registers

I have a question over this quote directly out of Computer Organization and Design, 5e: Signed versus unsigned applies to loads as well as to arithmetic. The function of a signed load is to copy ...
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2k views

Operating System: Performance of Demand Paging

I am reading Operating systems from the book "Operating System Concepts" by Peter Baer Galvin, 7th edition. Performance of Demand Paging: Let p be the probability of a page fault (0 $\leqslant$...
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117 views

Why TurnAround Time is considered as Performance Metric for Scheduling Algorithms?

I know what is turn around time but i am confused why wating time is not considred as Performance Metric for Scheduling Algorithms Since it gives the time for which a Process will wait till it gets ...
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42 views

If you increase the address space for an OS, does the Phys Mem used by the program increase?

I am learning about the OS. I know: that Address Space Size = # of pages x page size So if I increase Address Space Size, then the number of pages increases:(not the page size). However, isn't the ...
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1answer
2k views

What is “time-slice multi-threading”?

My goal is to understand the exact differences between SoEMT, SMT and "time-slice multi threading". Thus far I already found information on SoEMT and SMT and it does not seem to hard to find more on ...
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1answer
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Should we assume both processes are getting same CPU clock while we solve SYNCHRONIZATION problems in uniprocessor system?

In synchronization, when one process is in a critical section & another is busy waiting, both are using CPU. But in a uni processor system, in the same clock both cant get the CPU. So there must ...
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1answer
2k views

Process Synchronization: Dekker's algorithm

This Screenshot is taken from William Stalling's Operating Systems book. My doubt is that Bounded wait is not satisfied by this solution. For example: P0 and P1 both want to enter critical section ...
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4answers
8k views

Why do we need the valid-invalid bit in a page table?

I'm reading about memory management in Operating System Concepts, by A. Silberschatz. The author says: [...] the user process by definition is unable to access memory it does not own. It has no ...
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404 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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472 views

Convoy effect in priority scheduling and SJF (Non preemptive)

In books, I have read that FCFS suffers from convoy effect. I think that even SJF and priority(both preemptive and non preemptive) can suffer from convoy effect. In SJF, if a process with large burst ...
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1answer
56 views

Program counter format LC-2

Not really sure if this is an exact CS question. I'm reading the Patt/Patel Introduction to computing systems Powerpoint presentation and I don't understand about the program counter and instruction ...
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250 views

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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803 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
143 views

Numerator of HRRN scheduling formula

In the HRRN scheduling, priority formula is P = (W+E)/E , where W: waiting time and E: estimated run time. CPU finds the job that has highest priority value and does that job. However, the formula ...
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1answer
48 views

Is the term page replacement actually a misnomer?

My understanding is that "page replacement" entails replacing the contents of a frame to bring in a new frame in it's place corresponding to a new page. Since it is not the page, but the frame that ...
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67 views

What happens when accessing 0x00ABBA?

Given the following page table with a 24 Bit virtual address and 4KB page size and 4 byte long entries (%X means hexadecimal values): I don't understand how to translate e.g. address %X00ABBA here. I ...
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2k views

What is the difference between caching, buffering and paging? Expecting a detailed answer on the OS level

I have been reading about caching and buffering it seems about the same to me can't get hold of the differences clearly and paging, for now the only difference I understand between paging and caching ...
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What is the basic idea behind the usage of TLBs?

I know how Translation Lookaside Buffers work, and i also know we use them to improve the performance of data/program access by storing the recent page numbers - frame numbers in a memory cache. The ...