# Recent questions tagged galvin

1
Discuss the advantages and disadvantages of associating with remote file systems (stored on file servers) a set of failure semantics different from that associated with local file systems.
2
Some systems provide file sharing by maintaining a single copy of a file. Other systems maintain several copies, one for each of the users sharing the file. Discuss the relative merits of each approach
3
Discuss the advantages and disadvantages of supporting links to files that cross mount points (that is, the file link refers to a file that is stored in a different volume).
4
Give an example of an application that could benefit from operatingsystem support for random access to indexed files.
5
If the operating system knew that a certain application was going to access file data in a sequential manner, how could it exploit this information to improve performance?
6
Some systems automatically open a file when it is referenced for the first time and close the file when the job terminates. Discuss the advantages and disadvantages of this scheme compared with the more traditional one, where the user has to open and close the file explicitly
7
Provide examples of applications that typically access files according to the following methods: • Sequential • Random
8
Discuss the reasons why the operating system might require accurate information on how blocks are stored on a disk. How could the operating system improve file-system performance with this knowledge ?
9
Compare the performance of $C-SCAN$ and $SCAN$ scheduling, assuming a uniform distribution of requests. Consider the average response time (the time between the arrival of a request and the completion of that request’s service), the variation in response time, and the effective bandwidth. How does performance depend on the relative sizes of seek time and rotational latency ?
10
Suppose that a disk drive has $5,000$ cylinders, numbered $0$ to $4,999$. The drive is currently serving a request at cylinder $2,150$, and the previous request was at cylinder $1,805$. The queue of pending requests, in $FIFO$ ... for each of the following disk-scheduling algorithms ? $a. FCFS$ $b. SSTF$ $c. SCAN$ $d. LOOK$ $e. C-SCAN$ $f. C-LOOK$
11
Explain why $SSDs$(Solid State Drives) often use an $FCFS$ disk-scheduling algorithm.
12
None of the disk-scheduling disciplines, except $FCFS$, is truly fair (starvation may occur). a. Explain why this assertion is true. b. Describe a way to modify algorithms such as $SCAN$ to ensure fairness. c. Explain why fairness is an important goal in a ... d. Give three or more examples of circumstances in which it is important that the operating system be unfair in serving $I/O$ requests.
13
It is sometimes said that tape is a sequential-access medium, whereas a magnetic disk is a random-access medium. In fact, the suitability of a storage device for random access depends on the transfer size. The term streaming transfer rate denotes the rate for a data transfer that ... cache, memory, and tape. $f$. When is a tape a random-access device, and when is it a sequential-access device ?
14
Why is rotational latency usually not considered in disk scheduling ? How would you modify $SSTF$, $SCAN$, and $C-SCAN$ to include latency optimization ?
15
Explain why $SSTF$ scheduling tends to favor middle cylinders over the innermost and outermost cylinders.
16
Is disk scheduling, other than $FCFS$ scheduling, useful in a single-user environment ? Explain your answer.
1 vote
17
Consider a system that allocates pages of different sizes to its processes. What are the advantages of such a paging scheme ? What modifications to the virtual memory system provide this functionality ?
18
The slab-allocation algorithm uses a separate cache for each different object type. Assuming there is one cache per object type, explain why this scheme doesn’t scale well with multiple CPUs. What could be done to address this scalability issue?
19
A system provides support for user-level and kernel-level threads. The mapping in this system is one to one (there is a corresponding kernel thread for each user thread). Does a multithreaded process consist of $(a)$ a working set for the entire process or $(b)$ a working set for each thread ? Explain
20
Consider the parameter$\triangle$ used to define the working-set window in the working-set model. When $\triangle$ is set to a small value, what is the effect on the page-fault frequency and the number of active (non suspended) processes currently executing in the system ? What is the effect when $\triangle$ is set to a very high value ?
1 vote
21
Is it possible for a process to have two working sets, one representing data and another representing code ? Explain.
22
What is the cause of thrashing ? How does the system detect thrashing ? Once it detects thrashing, what can the system do to eliminate this problem ?
23
Consider a demand-paging system with a paging disk that has an average access and transfer time of $20$ milliseconds. Addresses are translated through a page table in main memory, with an access time of $1$ microsecond per memory access. Thus, each memory reference through ... those remaining, $10$ percent (or $2$ percent of the total) cause page faults. What is the effective memory access time?
1 vote
24
A page-replacement algorithm should minimize the number of page faults. We can achieve this minimization by distributing heavily used pages evenly over all of memory, rather than having them compete for a small number of page frames. We can associate with each page ... number of page faults for an optimal page replacement strategy for the reference string in part $b$ with four page frames?
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26
The open-file table is used to maintain information about files that are currently open. Should the operating system maintain a separate table for each user or maintain just one table that contains references to files that are currently being accessed by all users? If ... file is being accessed by two different programs or users, should there be separate entries in the open-file table? Explain.
27
Consider a file system in which a file can be deleted and its disk space reclaimed while links to that file still exist.What problems may occur if a new file is created in the same storage area or with the same absolute path name? How can these problems be avoided?