Operating Systems and CPU Scheduling Exam Questions

Operating System

A program that acts as an intermediary between the user and computer hardware.

Component of a Computer System

A part of a computer system, such as hardware, operating system, or application programs.

Primary Goal of an Operating System

To keep the CPU as busy as possible.

Role of an Operating System

Referee, Illusionist, Glue, All of the above.

Referee in Operating System

Resource allocation among users and applications.

Illusionist in Operating System

Creating the illusion of infinite resources.

Glue in Operating System

Providing libraries and user interface widgets.

Short-term Scheduler Purpose

To select processes from the ready queue and allocate the CPU.

Goal of an Operating System

To simplify the execution of user programs, use computer hardware efficiently, allow sharing of hardware and software resources, All of the above.

Importance of Studying Operating Systems

To understand the interaction between hardware and applications, develop new applications and hardware, understand basic principles in the design of computer systems, All of the above.

Primary Goal of Multiprogramming in CPU Scheduling

To keep the CPU as busy as possible.

NOT a Scheduling Criterion

Process termination time.

Convoy Effect in FCFS Scheduling

Short processes are stuck behind long processes.

Optimal Scheduling Algorithm for Minimizing Average Waiting Time

SJF.

Dispatch Latency

The time it takes for the dispatcher to switch processes.

CPU-I/O burst cycle

The alternating phases of CPU execution and I/O wait in a process

Short-term scheduler

To select processes from the ready queue and allocate the CPU

Preemptive scheduling

Scheduling where a process can be interrupted and replaced by another process

Nonpreemptive scheduling

Scheduling where a process cannot be interrupted

Dispatcher

To switch context between processes

CPU scheduler

To select the next process to run

CPU burst distribution

To predict the length of the next CPU burst

Histogram of CPU-burst times

To predict the length of the next CPU burst

Shortest-job-first (SJF) scheduling algorithm

To execute the process with the shortest burst time first

Challenge of implementing SJF scheduling

Predicting the next CPU burst length

Round-robin (RR) scheduling algorithm

To execute each process for a small unit of CPU time

Time quantum in round-robin scheduling

To allocate a small unit of CPU time to each process

Priority scheduling algorithm

To execute processes based on their priority

Challenge of priority scheduling

Starvation of low-priority processes

Aging in priority scheduling

To increase the priority of low-priority processes over time

MS-DOS `dir` command

Views the contents of a directory

cd command

Changes the current directory

md command

Creates a new directory

rd command

Deletes a directory

copy command

Copies a file

ren command

Renames a file

del command

Deletes a file

ver command

Displays the version of MS-DOS

/p switch in dir command

To pause after each screen of directory list information

/w switch in dir command

To display the directory list in wide format

average waiting time for FCFS scheduling with processes P1, P2, P3 and burst times 10, 5, 8

8.33

average waiting time for SJF scheduling with processes P1, P2, P3, P4 and burst times 7, 4, 2, 9

5.75

average waiting time for FCFS scheduling with processes P1, P2, P3 and burst times 12, 3, 6

9.67

average waiting time for SJF scheduling with processes P1, P2, P3 and burst times 12, 3, 6

4

average waiting time for round-robin scheduling with processes P1, P2, P3 and burst times 24, 3, 3, and time quantum 4

12.33

average waiting time for priority scheduling with processes P1, P2, P3, P4, P5 and burst times 10, 1, 2, 1, 5

8.2

purpose of the histogram of CPU-burst times

To predict the length of the next CPU burst

purpose of the system bus in a computer system

To connect the CPU to I/O devices

Memory Controller

To manage the memory

CPU

To execute instructions

Disk Controller

To manage the disk

Interrupt Service Routine (ISR)

To handle interrupts

Interrupt Vector Table

To handle interrupts

Dispatcher

To select the next process to run

Long-term Scheduler

To select processes from the pool of suspended processes and load them into memory

Medium-term Scheduler

To suspend processes that are not actively using the CPU

Process Abstraction

To represent an instance of a program running with limited rights

Address Space

To represent the set of accessible addresses

Dual-mode Operation

To differentiate between user mode and kernel mode

Timer

To interrupt the CPU after a specified period

Memory Protection

To prevent unauthorized access to memory

I/O Protection

To prevent unauthorized access to I/O devices

System Call Interface

To provide a controlled entry point to the kernel

Virtual Address

To provide the illusion of separate address spaces

Interrupt Handling Mechanism

To handle interrupts and switch to the interrupt service routine

Direct Memory Access (DMA)

To transfer data directly between memory and I/O devices