Questions tagged [operating-systems]

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

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1answer
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
289 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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2answers
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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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890 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
329 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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3answers
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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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1answer
93 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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27 views

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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1answer
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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1answer
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
86 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
409 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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0answers
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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0answers
302 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
315 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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124 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
162 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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0answers
67 views

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
450 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
494 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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2answers
3k views

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
424 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
129 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
624 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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1answer
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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113 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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2answers
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
45 views

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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390 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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460 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
55 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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0answers
247 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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1answer
787 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
139 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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1answer
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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1answer
70 views

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 ...
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1answer
736 views

Operating system maintains copy of page table for each process

I am quoting a paragraph in Operating System Concepts by Silberschatz, in paging chapter, In addition, the operating system must be aware that user processes operate in user space, and all ...
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5answers
233 views

Is Virtual Memory unreliable?

I have a question regarding multilevel page tables. As far as I know, in most 64 bit systems only 48 bits are used in page tables which would allow for 256TB of virtual memory to be addressed. For ...
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1answer
467 views

How is segmentation different from multiprogramming with fixed partition?

As seen here: It works same like multiprogramming with fixed partition and also the memory is contiguous as well. How is it different and especially non-contiguous? What's happening here?
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2answers
874 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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647 views

Since programs are swapped from backing store to main memory why don't they get lost when the computer is suddenly turned off?

So when I play a video, that means the video is moved from backing store to main memory. Then if I remove my laptop's battery all of sudden, that means the video should get lost as main memory is ...