Key Terms

Key Terms

access control list (ACL)

list of rules that specifies which users are granted the access to a specific object or resource

access enforcement

part of the OS that is responsible for enforcing access controls and protecting authentication and authorization information

address space

set of addresses generated by programs as they reference instructions and data

address translation

stage of virtualization that occurs when the system needs to find a physical address in the memory that matches the virtual address

allocation

method that defines how data is stored in the memory by providing a set of requests for resources and identifying which processes should be given which resources to make the most efficient use of the resources

application programming interface (API)

set of rules and tools that allows different software applications to communicate with each other

authentication

process of checking to see if a user’s credentials match the credentials in a database of authorized users or in a data authentication server

authorization

process of determining the relationship between principals, operations, and objects by defining which principals can perform which operations on which objects

badge

logical access system that serves as a form of authentication

blocked state

when a process is waiting for an event to occur

cache-only memory architecture (COMA)

computer memory architecture where all memory is treated as cache, which allows for the dynamic allocation of data for optimized access and performance in multiprocessor environments

capability list

list of objects and operations for each user that defines the user rights and capabilities

cloud infrastructure

virtualized and scalable hardware resources delivered over the Internet as a service

concurrency

multiple activities and processes happening at the same time—in other words, the OS handling multiple tasks at once

concurrent processing

computing model that improves the performance when multiple processors execute instructions simultaneously

condition variable

synchronization mechanism that is used in conjunction with locks to allow threads to wait for certain conditions to become true

container

standardized unit of software that logically isolates an application enabling it to run independently of physical resources

context switch

procedure that a computer’s CPU follows to change from one task to another while ensuring that the tasks do not conflict

CPU state

consists of the program counter (PC), the stack pointer (SP), and general-purpose registers

critical section

piece of code that only one thread can execute at once; also, only one thread at a time will get into this section of code

deadlock

synchronization challenge that occurs when a set of threads are blocked forever, waiting for each other to release resources

demand paging

storage mechanism in which pages should only allocate in the memory if it is required from the execution process

device manager

layer in the layered OS architecture that handles devices and provides buffering

device register

interface view any device presents to a programmer where each I/O device appears in the physical address space of the machine as a few words

directory

set of files that contains all the required information about the files such as attributes, location, and ownership, which is managed by the OS

distributed file system (DFS)

file system that is distributed on multiple file servers or multiple locations that support network-wide sharing of files and devices

dual mode

OS structure that is responsible for separating the user mode from the system mode

dynamic linking

code is located and loaded when the program is first run

encryption

method that converts the data into secret code that hides the data’s true meaning

exception

error that occurs at runtime

exokernel

OS architecture that simplifies the operating system by making its core (kernel) really small and letting apps have more control over the computer’s hardware

fault containment

feature of an OS that prevents errors in one part of an application from affecting the whole system

fault recovery

feature of an OS that helps the system to fix itself or revert to a previous state after an error

fault tolerance

feature of an OS that allows the application to keep running even when errors occur

file

collection of related information that is stored on secondary/virtual storage; it’s the smallest storage unit from the user’s perspective

file system

responsible for defining file names, storing files to a storage device, and retrieving files from storage devices

file versioning

system that allows a file to exist in several versions at the same time, which gives the user complete control over file creation

first come, first served (FCFS)

scheduling algorithm that operates on a simple queue mechanism where the first process to request the CPU is the first to receive it (or the first element added to the queue is the first one to be removed); commonly used in resource scheduling and data buffering and also known as FIFO (first in, first out)

fragmentation

problem where the memory blocks cannot be allocated to the processes due to their small size and the blocks remain unused

frame buffer

portion of random access memory (RAM) containing a bitmap that drives a video display

full virtualization

memory virtualization approach that allows multiple operating systems to run concurrently on a single physical machine, fully isolated from each other, by emulating hardware resources through a hypervisor

general-purpose register (GPR)

extra register that is used for storing operands and pointers

graphical user interface (GUI)

visual interface that allows users to interact with electronic devices through graphical icons and visual indicators

guest modification

in the context of virtualization, altering the guest operating system or its configuration to improve compatibility, performance, or integration with the virtualization environment or hypervisor

guest operating system

complete operating system inside a virtual machine

hardware abstraction layer (HAL)

example of layering in modern OS that allows an OS to interact with a hardware device at a general or abstract level rather than going deep into a detailed hardware level; this improves readability

heap allocation

dynamic storage management approach that allocates the data in a tree-based data structure

heap data

tree-based data in process management

hypervisor

software layer between machine hardware and the operating systems that run on it

i-number

unique number given to an inode whenever an OS that uses inodes creates a new file, which, in effect, functions as the file’s name

inconsistency

situation that causes the system to produce errors or hardware failure

incremental backup

backup image containing the pages that have been updated from the time of the previous backup

inode

structure used by file system that contains metadata about a file or directory but not its name

inter-process communication (IPC)

mechanism that enables processes to exchange data among different processes running on an operating system

interrupt

signal to the processor from either software or hardware that indicate events that need immediate attention

isolation

ensures that the multiple programs that are running concurrently on the same CPU and memory operate independently without interfering with each other’s execution or data

layered OS architecture

OS architecture where the OS is implemented as a set of layers where each layer exposes an enhanced virtual machine to the layer above

lock

synchronization mechanism that is used to enforce mutual exclusion

mechanism

activities that enforce policies and often depend on the hardware on which the operating system runs

memory allocation

process of setting aside sections of memory in a program to be used to store variables and instances of structures and classes

memory deallocation

process of freeing the space corresponding to finished processes when that space is needed by the rest of the system

memory multiplexing

dividing the capacity of the communication channel into multiple logical channels

microkernel

OS architecture where the functionality and capabilities are added to a minimal core OS as plug-ins

monolithic design

OS architecture where the entire OS is working in kernel space

multitasking

approach toward achieving concurrency that makes it possible for the OS to run multiple processes at the same time using time slicing

mutual exclusion

program that prevents simultaneous access to a shared resource

non-privileged system program

program that can run only in the user mode

non-uniform memory access (NUMA)

computer memory architecture where memory access time varies depending on the memory’s location relative to a processor

operating system (OS)

core piece of software that typically manages the interconnection of hardware and software on a given computer

page fault

when the CPU demands a page, and this page is not present in the main memory

page fetching

process of bringing pages into memory

page manager

layer in the layered OS architecture that implements virtual memories for each process

page replacement

when one page in the DRAM is swapped to disk while the requested page is brought into DRAM

paging

storage mechanism that uses a page form in retrieving process from secondary or virtual memory to main memory

pipe

data communication method between two processes that uses a specific name and standard I/O operations, and thus allows for data transfer within a file system; sometimes called named pipe

policy

controls how to use a mechanism in specific situations, that is, choose what activities need to be done

primary memory

type of computer memory that is the initial point of access for a processor and serves as direct storage for the CPU

primary storage

holds data that can be directly accessed by the CPU with minimum or no delay and does not survive a power failure

privileged instruction

instruction provided by the CPU that can be executed only by the OS

privileged system program

program that can run only in the system mode

process

any program that is running on top of the OS

process control block (PCB)

data structure used by the operating system to store information about a process, including its state, process ID, registers, scheduling information, memory management details, and I/O status

process ID (PID)

unique identifier assigned by the operating system to each process running on a computer, used to track and manage process activities

process synchronization

when an OS manages the sharing of a system’s resources to avoid interference and errors

properties

characteristics that are considered when designing an OS

protection

general mechanism that is used throughout the OS for all resources that need to be protected, such as memory, processes, files, devices, CPU time, and network bandwidth

quota

amount of space to store files based on the available memory space

ready state

when a process is waiting for the CPU

recovery

process of resolving or receiving treatment to solve OS faults or errors

reliability

system’s ability to reduce faults and ensure that the information in the system survives OS crashes and hardware failures

replication

procedure that allows multiple copies of a file to exist in the network; this improves performance and availability

round-robin scheduling (RR)

scheduling algorithm that is widely used in time-sharing systems and is designed to ensure fairness among processes by giving each process an equal share of the CPU

running state

when a process is being executed by the CPU

secondary memory

type of computer memory that is nonvolatile and thus used for long-term storage, housing the operating system, applications, and data that need to persist even when the power is off

secondary storage

persistent memory that survives power failures most of the time such as spinning disks, SSDs, and USB drives

semaphore

data type that an OS uses to control access to a resource

sharing

multiple processes can use the same piece of data concurrently

shortest remaining processing time (SRPT)

scheduling algorithm that prioritizes processes based on the shortest amount of time left to complete their execution

shortest time to completion first (STCF)

scheduling algorithm that takes the best approach to minimize the waiting time, but it requires that the processor knows the processing time in advance; also called shortest job first (SJF)

stack allocation

dynamic storage management approach that uses linear data structure that follows last in, first out (LIFO)

stack pointer (SP)

register that indicates the location of the last item that was added to the stack

static data

data that does not change within the program

synchronization

way of coordinating multiple concurrent activities that are using shared state

system call

appears when the program requests a service from the kernel

system interrupt

manages the communication between the computer hardware and the system

thrashing

when a computer’s operating system becomes overwhelmed by the number of processes requesting memory

thread

smallest unit of execution within a process, allowing parallel tasks to run in the same memory space; it enables efficient and independent execution of sequences of instructions

time slice

short time frame that gets assigned to a process for CPU execution and facilitates multitasking

translation lookaside buffer (TLB)

small memory cache that speeds up the computer’s memory access by storing recent virtual-to-physical address translations; if the TLB has the address translation, it quickly retrieves data; if not, the computer must search more slowly through its memory

two-factor authentication

form of authentication that involves two factors: the system calls or texts a user’s phone for the traditional password during login, employing the cell phone as a key

uniform memory access (UMA)

computer memory architecture where access time to any memory location is the same across all processors

virtual machine (VM)

software that is created to run like a physical computer and that operates its own operating system and applications like a separate physical server

virtualization

allows a system to run different types of applications used by multiple users at a time on the same computer

working set size (WSS)

total amount of memory a process requires during a specific period of activity; it is measured as the set of pages or data blocks the process accesses