89 Questions
What is the short definition of a process?
A process is a 'program in execution.'
What does the data section of a process contain?
Global variables
What is the key concept underlying modern operating system design?
A process
What type of activities does an operating system involve?
Asynchronous and sometimes parallel/concurrent
What is the address space of a process typically?
Virtual
In Round Robin scheduling, if there are 4 processes in the ready queue and the time quantum is 10 milliseconds, what is the maximum time any process has to wait to get CPU time?
40 milliseconds
If the burst times for processes P1, P2, P3, and P4 in Round Robin scheduling with time quantum 20 are 25, 15, 30, and 20 respectively, what is the completion time of process P3?
80 milliseconds
What is the purpose of Round Robin scheduling in interactive systems?
Minimize response time
In Round Robin scheduling, if the time quantum is very large, what effect does this have on short CPU burst processes?
They experience longer waiting times
How does the turnaround time of long CPU burst processes change in Round Robin scheduling?
It increases
Which event does not cause process creation?
Process termination
What is the purpose of the fork() system call in UNIX?
To create a new process as a clone of the parent process
What are the possible process states in an operating system?
Ready, running, blocked/waiting, new, terminated
How are processes created and deleted in an operating system?
Processes are created and deleted dynamically
What does the process control block (PCB) contain information about?
Computation, memory management, and file management
What are the benefits of using threads?
Low overhead context switching, resource sharing, economy, and utilization of multiprocessor architectures
What are the states that threads go through?
Ready, blocked, running, and terminated
What are the disadvantages of user-level threads?
Potential for any user-level thread to block the entire task if the kernel is single threaded
What are the types of thread implementations mentioned in the text?
Kernel-supported threads, user-level threads, and hybrid approaches
What is the role of kernel threads?
Supported and managed by the kernel, allowing explicit scheduling and parallel processing
What are some of the performance terms associated with scheduling?
Fairness, CPU and resource utilization, throughput
What are the scheduling objectives mentioned in the text?
Enforcing fairness, priorities, equipment utilization
What are some of the threading issues mentioned in the text?
Semantics of fork() and exec() system calls, handling of global variables
What does low-level scheduling involve?
Assigning a CPU to a ready process and selection from the ready queue
What is a characteristic of program behavior mentioned in the text?
CPU-I/O burst cycles
What is the main performance metric for FCFS scheduling?
Average waiting time
What is the preemptive version of Shortest-Job-First (SJF) scheduling known as?
Shortest-Remaining-Time-First (SRTF)
What technique can be used to solve the problem of starvation in priority scheduling?
Aging
In FCFS scheduling, what occurs when short processes wait behind long processes?
Convoy effect
What is the main goal of Shortest-Job-First (SJF) scheduling?
To schedule the process with the shortest next CPU burst
What does the data section of a process contain?
Global variables
What is the key concept underlying modern operating system design?
Process
What is the main goal of Shortest-Job-First (SJF) scheduling?
Minimize turnaround time
What are some of the threading issues mentioned in the text?
Thread safety
What type of activities does an operating system involve?
Asynchronous and parallel activities
In Round Robin (RR) scheduling, if there are 4 processes in the ready queue and the time quantum is 20 milliseconds, what is the maximum time any process has to wait to get CPU time?
80 milliseconds
What is the completion time of process P3 in Round Robin (RR) scheduling with time quantum 20, if the burst times for processes P1, P2, P3, and P4 are 25, 15, 30, and 20 respectively?
95 milliseconds
What is the main goal of Round Robin (RR) scheduling?
Minimize response time
What happens to the turnaround time of long CPU burst processes in Round Robin (RR) scheduling?
It usually becomes longer
What is the formula to calculate the maximum waiting time for any process in Round Robin (RR) scheduling?
$ (n-1) \times q $
What are the advantages of user-level threads?
Reduced context switch times and elimination of kernel overhead
What is a disadvantage of kernel threads compared to user-level threads?
Less control over scheduling and higher overhead
What is a characteristic of thread operations?
Creation, blocking, unblocking, and termination
What type of thread implementation reduces context switch times and eliminates kernel overhead?
User-level threads
How do multiple threaded processes enhance throughput and performance?
By allowing one thread to run while another is blocked and waiting
What is the purpose of the fork() system call in UNIX?
To create a new process as a clone of the parent process
What are the possible process states in an operating system?
New, running, blocked/waiting, ready, terminated
What is the main goal of Shortest-Job-First (SJF) scheduling?
To minimize the average waiting time for processes
What does the process control block (PCB) contain information about?
Computation, memory management, and file management
What are some of the threading issues mentioned in the text?
Concurrency, synchronization, and communication
What is the main performance metric for First Come First Serve (FCFS) scheduling?
Average waiting time
What is the preemptive version of Shortest-Job-First (SJF) scheduling known as?
Shortest-Remaining-Time-First (SRTF)
What problem may occur in priority scheduling and can be solved using aging?
Starvation
What is the term for the effect in FCFS scheduling when short processes wait behind long processes?
Convoy effect
What is the main goal of Shortest-Job-First (SJF) scheduling?
Minimize average waiting time
In Round Robin scheduling, how does an increase in the time quantum affect the waiting time of processes with long CPU burst times?
The waiting time decreases significantly
What is the main goal of high-level scheduling in batch systems?
Selecting a mix of CPU-bound and I/O-bound jobs
What is a critical issue related to threading and signal handling in threads?
Conflicts over the use of global variables
What are the program behavior characteristics mentioned in the text?
CPU-I/O burst cycles and histogram of CPU burst times
What is the primary concern regarding the semantics of fork() and exec() system calls in threading?
Proper creation and execution of new processes
______ issues include semantics of fork() and exec() system calls and handling of global variables like errno and malloc().
Threading
Conflicts between threads over the use of global variables can occur, potentially leading to errors and ______.
suspensions
Scheduling algorithm goals include high, intermediate, and ______ scheduling for batch systems.
low-level
Low-level scheduling, also called CPU scheduling, involves assigning a CPU to a ready process and selection from the ______ queue.
ready
Program behavior characteristics include CPU-I/O burst cycles, CPU/IO cycles, and histogram of CPU burst ______.
times
FCFS scheduling is ________ and uses FIFO queues
non-preemptive
Shortest-Job-First (SJF) scheduling aims to schedule the process with the ________ next CPU burst
shortest
Priority scheduling may lead to ________, and aging can be used as a solution to the problem
starvation
Determining the length of the next CPU burst involves guessing based on history using ________ averaging
exponential
Priority scheduling can be used in both ________ and interactive systems, with each job assigned a priority
batch
Multiple processes are executed concurrently with CPU ______ among them
multiplexing
Principal events causing process creation include system initialization, process creation system execution, user request, and ______ job initiation
batch
In UNIX, the fork() system call creates a new process as a clone of the parent process, while execve() system call replaces the process’ memory space with a new ______
program
Processes exist in a hierarchy forming a process group or process tree in many operating ______
systems
Processes are implemented through a process table or process control block (PCB) containing information about computation, memory management, and ______ management
file
An operating system executes a variety of programs: – Batch system – jobs – Time-shared systems – user programs or tasks Short definition: A process is a ______.
program in execution
A program is the code sitting in a file in this terminology. 3 Process Concept Multiple parts – The program code, also called text section – Current activity including program counter register and processor registers – Stack containing temporary data Function parameters, return addresses, local variables – Data section containing global variables – Heap containing memory dynamically allocated during run time (through new and malloc()). 4 Process in Memory Address space of a process (typically ______).
virtual
The notion of a software process is used in operating systems to express the management and control of such activities. A process is the key concept underlying modern operating system ______.
design
An operating system involves asynchronous, and sometimes parallel/concurrent, activities. The notion of a software process is used in operating systems to express the management and control of such activities. A process is the key concept underlying modern operating system ______.
design
Multithreading involves creating a new ______ for each HTTP request
process
Threads offer benefits such as low overhead context switching, resource sharing, economy, and utilization of ______ architectures
multiprocessor
In a single process, a thread shares its code section, data section, and OS resources with other ______
threads
Thread operations include creation, blocking, unblocking, and ______, similar to processes
termination
Multiple threaded processes enhance throughput and performance by allowing one thread to run while another is ______ and waiting
blocked
Each process in Round Robin scheduling gets 1/n of the CPU time in chunks of at most ______ time units at once.
$q$
Short CPU burst processes in Round Robin scheduling get their chance and exit the queue quickly when they are done, such as ______ tasks.
interactive
If the burst times for processes P1, P2, P3, and P4 in Round Robin scheduling with time quantum 20 are 25, 15, 30, and 20 respectively, the completion time of process P3 is ______.
77
In Round Robin scheduling, an increase in the time quantum ______ the waiting time of processes with long CPU burst times.
increases
In Round Robin scheduling, if there are 4 processes in the ready queue and the time quantum is 10 milliseconds, the maximum time any process has to wait to get CPU time is ______.
30
Study Notes
CPU Scheduling Algorithms Overview
- First Come First Serve (FCFS) policy allocates CPU to the first arriving process
- FCFS scheduling is non-preemptive and uses FIFO queues
- FCFS performance metric is the average waiting time
- FCFS scheduling example demonstrates Gantt chart visualization and average waiting time calculation
- Convoy effect in FCFS occurs when short processes wait behind long processes
- Shortest-Job-First (SJF) scheduling aims to schedule the process with the shortest next CPU burst
- SJF has non-preemptive and preemptive versions, with preemptive being known as Shortest-Remaining-Time-First (SRTF)
- Non-preemptive SJF example shows Gantt chart visualization and average waiting time calculation
- Preemptive SJF example demonstrates Gantt chart visualization and average waiting time calculation
- Determining the length of the next CPU burst involves guessing based on history using exponential averaging
- Priority scheduling can be used in both batch and interactive systems, with each job assigned a priority
- Priority scheduling may lead to starvation, and aging can be used as a solution to the problem.
Operating System Scheduling and Threading
- Solaris 2 and Windows NT/2000 with ThreadFiber package allow the operating system to create a sufficient number of kernel threads.
- Threading issues include semantics of fork() and exec() system calls and handling of global variables like errno and malloc().
- Signal handling in threads raises the question of which thread should catch the signals, especially in user-threads.
- Conflicts between threads over the use of global variables can occur, potentially leading to errors and suspensions.
- Processes and thread scheduling involves scheduling objectives for batch, interactive, and real-time systems.
- Scheduling objectives include enforcing fairness, priorities, equipment utilization, and preference to processes exhibiting good behavior.
- Performance terms associated with scheduling include fairness, CPU and resource utilization, throughput, turnaround time, waiting time, and response time.
- Program behavior characteristics include CPU-I/O burst cycles, CPU/IO cycles, and histogram of CPU burst times.
- Scheduling algorithm goals include high, intermediate, and low-level scheduling for batch systems.
- High-level scheduling involves selecting a mix of CPU-bound and I/O-bound jobs and alternate selection criteria.
- Intermediate scheduling involves temporarily suspending or resuming jobs to smooth fluctuations in system load.
- Low-level scheduling, also called CPU scheduling, involves assigning a CPU to a ready process and selection from the ready queue.
Multithreading: Types, Models, and Usage
- Multithreading involves creating a new process for each HTTP request, but this can lead to high overhead.
- Threads offer benefits such as low overhead context switching, resource sharing, economy, and utilization of multiprocessor architectures.
- In a single process, a thread shares its code section, data section, and OS resources with other threads.
- Thread usage examples include a word processor with three threads for input, reformat, and save, as well as graphics applications like augmented reality.
- Thread operations include creation, blocking, unblocking, and termination, similar to processes.
- Threads go through states like ready, blocked, running, and terminated, and they are considered cooperating with no protection among threads.
- Multiple threaded processes enhance throughput and performance by allowing one thread to run while another is blocked and waiting.
- Extensive sharing in threads makes CPU switching and thread creation inexpensive compared to heavyweight processes.
- There are different types of thread implementations including kernel-supported threads, user-level threads, and hybrid approaches.
- User-level threads are managed by a user-level threads library, reducing context switch times and eliminating kernel overhead.
- Disadvantages of user-level threads include the potential for any user-level thread to block the entire task if the kernel is single threaded.
- Kernel threads are supported and managed by the kernel, allowing explicit scheduling and parallel processing, but with less control over scheduling and higher overhead compared to user-level threads.
Test your knowledge of CPU scheduling algorithms with this quiz. Explore First Come First Serve (FCFS), Shortest-Job-First (SJF), and Priority scheduling, and learn about their features, performance metrics, and potential issues. Dive into examples with Gantt chart visualizations and average waiting time calculations to deepen your understanding of these essential algorithms.
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