Os Final

Front 1

The operating system kernel consists of all system and application programs in a computer.

Back 1

False

Front 2

Flash memory is slower than DRAM but needs no power to retain its contents.

Back 2

True

Front 3

A system call is triggered by hardware.

Back 3

False

Front 4

UNIX does not allow users to escalate privileges to gain extra permissions for a restricted activity.

Back 4

False

Front 5

Processors for most mobile devices run at a slower speed than a processor in a desktop PC.

Back 5

True

Front 6

Interrupts may be triggered by either hardware or software.

Back 6

True

Front 7

A dual-core system requires each core has its own cache memory.

Back 7

False

Front 8

Virtually all modern operating systems provide support for symmetric multiprocessing(SMP).

Back 8

True

Front 9

All computer systems have some sort of user interaction.

Back 9

False

Front 10

Solid state disks are generally faster than magnetic disks.

Back 10

True

Front 11

Solid state disks are considered volatile storage.

Back 11

False

Front 12

There is no universally accepted definition of an operating system.

Back 12

True

Front 13

The __________ of a process contains temporary data such as function parameters, return addresses, and local variables.

Back 13

Stack

Front 14

A process control block __________.

Back 14

Includes information on the process's state

Front 15

The list of processes waiting for a particular I/O decide is called a __________.

Back 15

Device queue

Front 16

The __________ refers to the number of processes in memory.

Back 16

Degree of multiprogramming

Front 17

When a child process is created, which of the following is a possibility in terms of the execution or address space of the child process?

Back 17

The child process runs concurrently with the parent.

The child process has a new program loaded into it.

The child is a duplicate of the parent.

Front 18

A __________ saves the state of the currently running process and restores the state of the next process to run.

Back 18

Context switch

Front 19

Which of the following statements is true?

Back 19

Shared memory is typically faster than message passing.

Front 20

Imagine that a host with IP address 150.55.66.77 wishes to download a file from the web server at IP address 202.28.15.123. Select a valid socket pair for a connection between this pair of hosts.

Back 20

150.55.66.77:2000 & 202.28.15.123:80

Front 21

For a single-processor system, there will never be more than one process in the running state.

Back 21

True

Front 22

Shared memory is a more appropriate IPC mechanism than message passing for distributed systems.

Back 22

False

Front 23

Ordinary pipes in UNIX require a parent-child relationship between the communicating processes.

Back 23

True

Front 24

A socket is identified by an IP address concatenated with a port number.

Back 24

True

Front 25

Pthreads refers to a __________.

Back 25

Specification for thread behavior

Front 26

The __________ multithreading model multiplexes many user-level threads to a smaller or equal number of kernel threads.

Back 26

Many-to-many model

Front 27

Cancellation points are associated with __________ cancellation.

Back 27

Deferred

Front 28

Thread-local storage is data that __________.

Back 28

Is unique to each thread

Front 29

__________ is not considered a challenge when designing applications for multicore systems.

Back 29

Ensuring there is a sufficient number of cores

Front 30

A __________ provides an API for creating and managing threads.

Back 30

Thread library

Front 31

The __________ model multiplexes many user-level threads to a smaller or equal number of kernel threads.

Back 31

Many-to-many

Front 32

A traditional (or heavyweight) process has a single thread of control.

Back 32

True

Front 33

A thread is composed of a thread ID, program counter, register set, and heap.

Back 33

False

Front 34

Virtually all contemporary operating systems support kernel threads.

Back 34

True

Front 35

Each thread has its own register set and stack.

Back 35

True

Front 36

Deferred cancellation is preferred over asynchronous cancellation.

Back 36

True

Front 37

The single benefit of a thread pool is to control the number of threads.

Back 37

False

Front 38

It is possible to create a thread library without any kernel-level support.

Back 38

True

Front 39

What is the better locking mechanism when the lock is to be held for a short duration?

Back 39

Spinlock

Front 40

What is the better locking mechanism when the lock is to be held for a long duration?

Back 40

Mutexlock

Front 41

What is the better locking mechanism when the thread may be put to sleep while holding the lock?

Back 41

Mutexlock

Front 42

Assume you have a mutex lock named mutex with the operations acquire() and release(). Indicate where the locking needs to be placed to prevent the race condition(s).

Back 42

A call to acquire() must be placed upon entering each function and a call to release() immediately before exiting each function.

Front 43

A race condition ____________.

Back 43

Results when several threads try to access and modify the same data concurrently

Front 44

An instruction that executes atomically ____________.

Back 44

Executes as a single, uninterruptible unit

Front 45

A counting semaphore ____________.

Back 45

Is essentially an integer variable

Front 46

A mutex lock ____________.

Back 46

Is essentially a boolean variable

Front 47

In Peterson's solution, the ____________ variable indicates if a process is ready to enter its critical section.

Back 47

flag[i]

Front 48

A ____________ type presents a set of programmer-defined operations that are provided mutual exclusion within it.

Back 48

Monitor

Front 49

What is the correct order of operations for protecting a critical section using mutex locks?

Back 49

Acquire() followed by release()

Front 50

What is the correct order of operations for protecting a critical section using a binary semaphore?

Back 50

Wait() followed by signal()

Front 51

____________ is not a technique for handling critical sections in operating systems.

Back 51

Peterson's solution

Front 52

A solution to the critical section problem does not have to satisfy which of the following requirements?

Back 52

Atomicity

Front 53

A ____________ refers to where a process is accessing/updating shared data.

Back 53

Critical section

Front 54

Spinlocks can be used to prevent busy waiting in the implementation of semaphore.

Back 54

True

Front 55

What three conditions must be satisfied in order to solve the critical section problem?

Back 55

No thread executing in its critical section, if one already is.

Only threads not executing in their critical section decide which enters next.

The number of times other threads enter their critical states, after a thread makes a request, must be bound.

Front 56

Explain two general approaches to handle critical sections in operating systems.

Back 56

Preemptive Kernel: Allows a process to be preempted while it is running in kernel mode.

Non Preemptive Kernel: Does not allow a process to be preempted while it is running in kernel mode. Basically free from race conditions.

Front 57

Which of the following is true of cooperative scheduling?

Back 57

A process keeps the CPU until it releases the CPU either by terminating or by switching to the waiting state.

Front 58

____________ is the number of processes that are completed per time unit.

Back 58

Throughput

Front 59

____________ scheduling is approximated by predicting the next CPU burst with an exponential average of the measured lengths of previous CPU bursts.

Back 59

SJF

Front 60

The ____________ scheduling algorithm is designed especially for time-sharing systems.

Back 60

RR

Front 61

Which of the following scheduling algorithms must be non-preemptive?

Back 61

FCFS

Front 62

Which of the following is true of multilevel queue scheduling?

Back 62

Each queue has its own scheduling algorithm

Front 63

The ____________ occurs in first-come-first-served scheduling when a process with a long CPU burst occupies the CPU.

Back 63

Convoy effect

Front 64

In Little’s formula, λ represents the ___________.

Back 64

Average arrival rate for new processes in the queue

Front 65

__________ allows a thread to run on only one processor.

Back 65

Processor affinity

Front 66

_________ involves the decision of which kernel thread to schedule onto which CPU.

Back 66

System-contention scope

Front 67

A significant problem with priority scheduling algorithms is _______.

Back 67

Starvation

Front 68

The rate of a periodic task in a hard real-time system is _____, where p is a period and t is the processing time.

Back 68

1/p

Front 69

Which of the following is true of the rate-monotonic scheduling algorithm?

Back 69

CPU utilization is bounded when using this algorithm

Front 70

Which of the following is true of the EDF scheduling algorithm?

Back 70

When a process becomes runnable, it must announce its deadline requirements to the system

Front 71

The two general approaches to load balancing are _____ and _____.

Back 71

Push migration, pull migration

Front 72

What are the two types of latency that affect the performance of real-time systems?

Back 72

Interrupt latency and dispatch latency

Front 73

What are the advantages of the EDF scheduling algorithm over the rate-monotonic scheduling algorithm?

Back 73

EDF does not require a constant period or burst time. It is theoretically optimal.

Front 74

A deadlocked state occurs whenever _________.

Back 74

Every process in a set is waiting for an event that can only be caused by another process in the set

Front 75

One necessary condition for deadlock is ____, which states that at least one resource must be held in a nonsharable mode.

Back 75

Mutual exclusion

Front 76

One necessary condition for deadlock is ______, which states that a process must be holding one resource and waiting to acquire additional resources.

Back 76

Hold and wait

Front 77

In a system resources-allocated graph, _________.

Back 77

A directed edge from a process to a resource is called a request edge

Front 78

A cycle in a resource-allocation graph is _________.

Back 78

A necessary and sufficient condition for deadlock in the case that each resource has exactly one instance

Front 79

To handle deadlocks, the OS will most often __________.

Back 79

Pretend that deadlocks never occur

Front 80

Assume there are three resources, R1, R2, R3, that are each assigned unique integer values 15, 10, and 25 respectively. What is a resource ordering which prevents circular waiting?

Back 80

R2, R1, R3

Front 81

Explain what has to happen for a set of processes to achieve a deadlocked state.

Back 81

All four deadlock conditions must be satisfied simultaneously

Front 82

Describe the four conditions that must hold simultaneously in a system if a deadlock is to occur.

Back 82

Mutual exclusion - 1 process to 1 resource at a time

Hold and wait - a process holding a resource is waiting to acquire additional resources Circular wait - a series of processes that are waiting for the next process to release its resource

No preemption - a resource can only be released voluntarily by the process holding it

Front 83

What is the difference between deadlock prevention and deadlock avoidance?

Back 83

Deadlock prevention - 1 of the 4 conditions for deadlock to occur is not true

Deadlock avoidance - additional information is needed to determine if deadlock will occur

Front 84

What is one way to ensure that a circular-wait condition does not occur?

Back 84

Ordering - give each process a unique number

Front 85

Describe two methods for eliminating processes by aborting a process.

Back 85

Abort all processes at once

Abort one process at a time until all processes are aborted

Front 86

An address generated by a CPU is referred to as a ________.

Back 86

Logical address

Front 87

The mapping of a logical address to a physical address is done in hardware by the ______.

Back 87

MMU

Front 88

The _____ binding scheme facilitates swapping.

Back 88

Execution time

Front 89

________ is the dynamic storage-allocation algorithm which results in the smallest leftover hole in memory.

Back 89

Best fit

Front 90

Which of the following is true of compaction?

Back 90

It is possible only if relocation is dynamic and done at execution time

Front 91

Assume a system has a TLB hit ratio of 90%. It requires 15 nanoseconds to access the TLB, and 85 nanoseconds to access main memory. What is the effective memory access time in nanoseconds for this system? (HR * TT) + (MR * (MMT + TT))

Back 91

108.5

Front 92

Given the logical address 0xAEF9 (in hexadecimal) with a page size of 256 bytes, what is the page number?

Back 92

0xAE

Front 93

With segmentation, a logical address consists of ___________.

Back 93

Segment number and offset

Front 94

A(n) _____ matches the process with each entry in the TLB.

Back 94

Address-space identifier

Front 95

Distinguish between internal and external fragmentation.

Back 95

Internal - wasted space due to the block of data loaded being smaller than the partition. Internal fragmentation is eliminated by segmentation

External - memory becomes more and more fragmented; memory utilization declines

Front 96

Explain the basic method for implementing paging.

Back 96

Partition memory into equal fixed-size chunks that are relatively small

Process is also divided into small fixed-size chunks of the same size

Front 97

What is the difference between simple paging and virtual memory paging?

Back 97

Simple - All pages are loaded into main memory Virtual memory - Few pages are loaded at the same time into main memory

Front 98

Explain thrashing

Back 98

Thrashing is a state in which the system spends most of its time swapping process pieces rather than executing instructions.

To avoid this, the OS tries to guess which pieces are least likely to be used in the near future. Guess is based on recent history.

Front 99

What elements are typically found in a page table entry? Briefly define each element.

Back 99

Frame number - sequential page number in main memory

Present bit - indicates if page is in main memory

Modify bit - indicates if page has been modified since coming to main memory

Front 100

What is the purpose of a translation lookaside buffer (TLB)?

Back 100

A cache that helps avoid going to the disk to retrieve a page. This decreases memory access time.

Front 101

Which of the following is a benefit of allowing a program that is only partially in memory to execute?

Back 101

Programs can be written to use more memory than is available in physical memory

CPU utilization and throughput is increased

Less I/O is needed to load or swap each user program into memory

Front 102

In systems that support virtual memory, ______.

Back 102

Physical memory is separated from logical memory

Front 103

Belady’s anomaly states that _________.

Back 103

For some page replacement algorithms, the page-fault rate may increase as the number of allocated frames increases

Front 104

__________ allows the parent and child processes to initially share the same pages, but when either process modifies a page, a copy of the shared page is created.

Back 104

Copy-on-write

Front 105

__________ is the algorithm implemented on most systems.

Back 105

LRU

Front 106

________ occurs when a process spends more time paging than executing.

Back 106

Thrashing