WGU d686 Operating Systems for Computer Scientists questions with 100% correct answers + rationales(PASSED)

operating system

software that manages a computer's hardware. It also provides a basis for application programs and acts as an intermediary between the computer user and the computer hardware.

hardware

the central processing unit (CPU), the memory, and the input/output (I/O) devices—provides the basic computing resources for the system.

application programs

such as word processors, spreadsheets, compilers, and web browsers—define the ways in which these resources are used to solve users' computing problems.

environment

An operating system is similar to a government. Like a government, it performs no useful function by itself. It simply provides an environment within which other programs can do useful work.

 kernel

the main part of an operating system that starts running as soon as a computer turns on

system program

software related to the operating system but designed for smaller and more specific tasks . (Utility Software)

Bus

A communication system; e.g., within a computer, a bus connects various components, such as the CPU and I/O devices, allowing them to transfer data and commands.

device driver

An operating system component that provides uniform access to various devices and manages I/O to those devices.

interrupt

A hardware mechanism that enables a device to notify the CPU that it needs attenti

interrupt vector

An operating-system data structure indexed by interrupt address and pointing to the interrupt handlers. A kernel memory data structure that holds the addresses of the interrupt service routines for the various devices.

interrupt-request line

The hardware connection to the CPU on which interrupts are signaled.

interrupt-handler routine

An operating system routine that is called when an interrupt signal is received.

interrupt-controller hardware

Computer hardware components for interrupt management

nonmaskable interrupt

An interrupt that cannot be delayed or blocked (such as an unrecoverable memory error)

maskable

Describes an interrupt that can be delayed or blocked (such as when the kernel is in a critical section).

interrupt chaining

A mechanism by which each element in an interrupt vector points to the head of a list of interrupt handlers, which are called individually until one is found to service the interrupt request.

interrupt priority level

Prioritization of interrupts to indicate handling order.

bootstrap program

the first program that starts a computer by getting everything ready for the main software to run when the computer is turned on

electrically erasable programmable read-only memory (EEPROM)

a type of nonvolatile memory that can be electrically erased and reprogrammed to store data

Memory Device Types (review)

hard disk drive (HDD): a storage device that uses spinning disks and read/write heads to store and retrieve data 

nonvolatile memory (NVM): memory that retains data even when power is turned off 

nonvolatile storage (NVS): storage that keeps data without needing power, such as hard drives and SSDs

solid state drive (SSD): a storage device that uses flash memory to store data with no moving parts 

random-access memory (RAM): a computer's main memory that can be used quickly to run programs 

dynamic random-access memory (DRAM): a type of RAM that is fast and used a lot in computers  

User Mode

refers to the CPU operating mode that restricts certain instructions from executing user processes

kernel mode

refers to a CPU operating mode where all instructions are accessible

mode bit

added to the hardware of the computer to indicate the current mode: kernel (0) or user (1). With the mode bit, we can distinguish between a task that is executed on behalf of the operating system and one that is executed on behalf of the user.

privileged instructions

The hardware allows privileged instructions to be executed only in kernel mode.

switch to kernel mode is an example of a privileged instruction. Some other examples include I/O control, timer management, and interrupt management

protection rings

A model of privilege separation consisting of a series of rings, with each successive ring representing greater execution privileges.

virtual machine manager

The computer function that manages the virtual machine; also called a hypervisor.

Has privileged access somewhere between User and Kernel

timer

A hardware component that can be set to interrupt the computer after a specified period.

batch operating system

executes similar jobs in batches to optimize CPU use without user interaction

multiprogramming

keeps multiple programs in memory to maximize CPU usage by switching between them

time-sharing system

n operating system that allows multiple users to share computer resources simultaneously

real-time system

ensures tasks are completed within defined time limits, including hard (strict) and soft (flexible) real-time systems

hard real-time

handles critical tasks that must meet strict, predefined time constraints without virtual memory or time-sharing

soft real-time

handles tasks with deadlines that are more flexible than hard real-time systems, allowing for some timing variability

distributed operating system

handles networked processors that collaborate on tasks, enabling resource sharing and high-speed processing

loosely coupled systems

systems where each component or computer is independent and communicates over a network

fault tolerance

the ability of a multiprocessor system to handle the failure of a processor by redistributing its tasks to other processors, ensuring continuous operation

resource manager

The system's CPU, memory space, file-storage space, and I/O devices are among the resources that the operating system must manage

I/O subsystem

The I/O subsystem consists of several components:

A memory-management component that includes buffering, caching, and spooling

A general device-driver interface

Drivers for specific hardware devices

shared memory

In interprocess communication, a section of memory shared by multiple processes and used for message passing.

message passing

In interprocess communication, a method of sharing data in which messages are sent and received by processes. Packets of information in predefined formats are moved between processes or between computers.

command interpreter

The operating system component that interprets user commands and causes actions based on them.

shells

One of the command interpreters on a system with multiple command interpreters to choose from.

shell scripts

A file containing a set series of commands (similar to a batch file) that are specific to the shell being used.

System calls

Software-triggered interrupt allowing a process to request a kernel service.

process control

Definition: A running program needs to halt its execution either normally or abnormally.

create process, terminate process

load, execute

get process attributes, set process attributes

wait event, signal event

allocate and free memory

file management

Definition: Managing files includes creating, deleting, opening, reading, writing, and closing.

create file, delete file

open, close

read, write, reposition

get file attributes, set file attributes

device management

Definition: Managing physical and virtual devices

request device, release device

read, write, reposition

get device attributes, set device attributes

logically attach or detach devices

information maintenance

Definition: Transferring information between user programs and the operating system

get time or date, set time or date

get system data, set system data

get process, file, or device attributes

set process, file, or device attributes

communications

Definition: Enabling processes to exchange information

create, delete communication connection

send, receive messages

transfer status information

attach or detach remote devices

protection

Definition: Controlling access to computer system resources

get file permissions

set file permissions

application programming interface (API)

A set of commands, functions, and other tools that can be used by a programmer in developing a program.

These APIs allow developers to write portable code that can run on any system supporting the same API.

runtime environment (RTE)

handles these system calls, using a system-call interface

system-call interface

translates API functions into kernel-level operations

6 Types of System Calls

Process Control

File Management

Device Management Information Maintenance

Communication

Protection

symmetric multiprocessing (SMP)

each peer CPU processor performs all tasks, including operating-system functions and user processes

clustered system

A system that gathers together multiple CPUs. Clustered systems differ from multiprocessor systems in that they are composed of two or more individual systems—or nodes—joined together.

high-availability

Describes a service that will continue even if one or more systems in the cluster fail.

graceful degradation

The ability of a system to continue providing service proportional to the level of surviving hardware.

fault-tolerant system

A system that can suffer a failure of any single component and still continue operation.

asymmetric clustering

A configuration in which one machine in a cluster is in hot-standby mode while the other is running applications.

hot-standby mode

A condition in which a computer in a cluster does nothing but monitor the active server. If that server fails, the hot-standby host becomes the active server.

symmetric clustering

A situation in which two or more hosts are running applications and are monitoring each other.

distributed lock manager (DLM)

A function used by a clustered system to supply access control and locking to ensure that no conflicting operations occur.

storage-area network (SAN)

A local-area storage network allowing multiple computers to connect to one or more storage devices.

System services

also known as system utilities, provide a convenient environment for program development and execution. Some of them are simply user interfaces to system calls. Others are considerably more complex.

7 Examples of System Services

File management

Status Information

File modification

Programming Language Support

Program Loading and Execution

Communications

Background Services

system utility

A collection of applications included with or added to an operating system to provide services beyond what are provided by the kernel.

registry

A file, set of files, or service used to store and retrieve configuration information. In Windows, the manager of hives of data.

service

A software entity running on one or more machines and providing a particular type of function to calling clients. In Android, an application component with no user interface; it runs in the background while executing long-running operations or performing work for remote processes.

subsystem

A subset of an operating system responsible for a specific function (e.g., memory management).

application program

A program designed for end-user execution, such as a word processor, spreadsheet, compiler, or Web browser.

monolithic structure

Singe static binary file, changes affect entire structure.

layered approach

The main advantage of the layered approach is simplicity of construction and debugging

microkernel

his method structures the operating system by removing all nonessential components from the kernel and implementing them as user-level programs that reside in separate address spaces.

Advantage: is easier to port from one hardware design to another. The microkernel also provides more security and reliability, since most services are running as user—rather than kernel—processes. If a service fails, the rest of the operating system remains untouched.

loadable kernel module (LKM)

A kernel structure in which the kernel has a set of core components and can link in additional services via modules, either at boot time or during run time.

application frameworks layer

n the layered macOS and iOS operating system design, the layer that includes Cocoa and Cocoa Touch frameworks, providing an API for Objective-C and Swift programming languages.

kernel environment

in the layered macOS and iOS operating system design, the darwin layer that includes the mach microkernel and the bsd unix kernel.

Mach

An operating system with microkernel structure and threading; developed at Carnegie Mellon University.

Process State

As a process executes, it changes state. The state of a process is defined in part by the current activity of that process. A process may be in one of the following states:

New. The process is being created.

Running. Instructions are being executed.

Waiting. The process is waiting for some event to occur (such as an I/O completion or reception of a signal).

Ready. The process is waiting to be assigned to a processor.

Terminated. The process has finished execution.

Process Control Block

serves as the repository for all the data needed to start, or restart, a process, along with some accounting data.

Process State

Program Counter

CPU Registers

CPU scheduling info

Memory Management info

Accounting info

I/O status info

task

A process, a thread activity, or, generally, a unit of computation on a computer.

text section

The executable code of a program or process.

data section

The data part of a program or process; it contains global variables.

heap section

The section of process memory that is dynamically allocated during process run time; it stores temporary variables.

stack section

The section of process memory that contains the stack; it contains activation records and other temporary data.

activation record

record created when a function or subroutine is called; added to the stack by the call and removed when the call returns. Contains function parameters, local variables, and the return address.

task control block

A per-process kernel data structure containing many pieces of information associated with the process.

thread

A process control structure that is an execution location. A process with a single thread executes only one task at a time, while a multithreaded process can execute a task per thread.

process scheduler

A scheduler that selects an available process (possibly from a set of several processes) for execution on a CPU.

degree of multiprogramming

The number of processes in memory.

I/O-bound process

A process that spends more of its time doing I/O than doing computations

CPU-bound process

A process that spends more time executing on CPU than it does performing I/O

ready queue

The set of processes ready and waiting to execute.

wait queue

In process scheduling, a queue holding processes waiting for an event to occur before they need to be put on CPU.

dispatched

Selected by the process scheduler to be executed next.

CPU scheduler

Kernel routine that selects a thread from the threads that are ready to execute and allocates a core to that thread.

foreground

Describes a process or thread that is interactive (has input directed to it), such as a window currently selected as active or a terminal window currently selected to receive input.

background:

Describes a process or thread that is not currently interactive (has no interactive input directed to it), such as one not currently being used by a user. In the Grand Central Dispatch Apple OS scheduler, the scheduling class representing tasks that are not time sensitive and are not visible to the user.

split-screen

Running multiple foreground processes (e.g., on an iPad) but splitting the screen among the processes.

service

A software entity running on one or more machines and providing a particular type of function to calling clients. In Android, an application component with no user interface; it runs in the background while executing long-running operations or performing work for remote processes.