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reliability : systemâs ability to reduce faults and ensure that the information in the system survives OS crashes and hardware failures | https://openstax.org/books/introduction-computer-science/pages/6-key-terms |
replication : procedure that allows multiple copies of a file to exist in the network; this improves performance and availability | https://openstax.org/books/introduction-computer-science/pages/6-key-terms |
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 | https://openstax.org/books/introduction-computer-science/pages/6-key-terms |
running state : when a process is being executed by the CPU | https://openstax.org/books/introduction-computer-science/pages/6-key-terms |
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 | https://openstax.org/books/introduction-computer-science/pages/6-key-terms |
secondary storage : persistent memory that survives power failures most of the time such as spinning disks, SSDs, and USB drives | https://openstax.org/books/introduction-computer-science/pages/6-key-terms |
semaphore : data type that an OS uses to control access to a resource | https://openstax.org/books/introduction-computer-science/pages/6-key-terms |
sharing : multiple processes can use the same piece of data concurrently | https://openstax.org/books/introduction-computer-science/pages/6-key-terms |
shortest remaining processing time (SRPT) : scheduling algorithm that prioritizes processes based on the shortest amount of time left to complete their execution | https://openstax.org/books/introduction-computer-science/pages/6-key-terms |
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) | https://openstax.org/books/introduction-computer-science/pages/6-key-terms |
stack allocation : dynamic storage management approach that uses linear data structure that follows last in, first out (LIFO) | https://openstax.org/books/introduction-computer-science/pages/6-key-terms |
stack pointer (SP) : register that indicates the location of the last item that was added to the stack | https://openstax.org/books/introduction-computer-science/pages/6-key-terms |
static data : data that does not change within the program | https://openstax.org/books/introduction-computer-science/pages/6-key-terms |
synchronization : way of coordinating multiple concurrent activities that are using shared state | https://openstax.org/books/introduction-computer-science/pages/6-key-terms |
system call : appears when the program requests a service from the kernel | https://openstax.org/books/introduction-computer-science/pages/6-key-terms |
system interrupt : manages the communication between the computer hardware and the system | https://openstax.org/books/introduction-computer-science/pages/6-key-terms |
thrashing : when a computerâs operating system becomes overwhelmed by the number of processes requesting memory | https://openstax.org/books/introduction-computer-science/pages/6-key-terms |
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 | https://openstax.org/books/introduction-computer-science/pages/6-key-terms |
time slice : short time frame that gets assigned to a process for CPU execution and facilitates multitasking | https://openstax.org/books/introduction-computer-science/pages/6-key-terms |
translation lookaside buffer (TLB) : small memory cache that speeds up the computerâs 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 | https://openstax.org/books/introduction-computer-science/pages/6-key-terms |
two-factor authentication : form of authentication that involves two factors: the system calls or texts a userâs phone for the traditional password during login, employing the cell phone as a key | https://openstax.org/books/introduction-computer-science/pages/6-key-terms |
uniform memory access (UMA) : computer memory architecture where access time to any memory location is the same across all processors | https://openstax.org/books/introduction-computer-science/pages/6-key-terms |
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 | https://openstax.org/books/introduction-computer-science/pages/6-key-terms |
virtualization : allows a system to run different types of applications used by multiple users at a time on the same computer | https://openstax.org/books/introduction-computer-science/pages/6-key-terms |
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 | https://openstax.org/books/introduction-computer-science/pages/6-key-terms |
An operating system (OS) is at the core of all of the connected hardware and software. | https://openstax.org/books/introduction-computer-science/pages/6-summary |
Improving efficiency results in speeding up the implementation of applications from coding time and runtime standpoints. OSs have a large influence because of the abstractions/interfaces they implement. | https://openstax.org/books/introduction-computer-science/pages/6-summary |
Operating systems provide both mechanism and policy. Mechanism refers to a set of activities that you can do. Policy is how to use the mechanism in specific situations. | https://openstax.org/books/introduction-computer-science/pages/6-summary |
Virtualization in an operating system allows the system to run different applications that are handled by multiple users at a time on the same computer. | https://openstax.org/books/introduction-computer-science/pages/6-summary |
Server virtualization places a software layer called a hypervisor (e.g., virtual machine monitor or VMM) between a machine (e.g., server) hardware and the operating systems that run on it. | https://openstax.org/books/introduction-computer-science/pages/6-summary |
Using OS-level or server virtualization allows a server to run different types of operating systems at the same time on the same computer. | https://openstax.org/books/introduction-computer-science/pages/6-summary |
The OS translates from the hardware interface to the application interface and provides each running program with its own process. | https://openstax.org/books/introduction-computer-science/pages/6-summary |
A process consists of address space, one or more threads of control executing in that address space, and additional system state associated with it. The thread is a path of execution within a process and a process may contain multiple threads. | https://openstax.org/books/introduction-computer-science/pages/6-summary |
The instruction set architecture (ISA) defines a set of instructions that can be used to write assembly language programs that use the CPU while abstracting the hardware details from the program. | https://openstax.org/books/introduction-computer-science/pages/6-summary |
OS functions guarantee protection, isolation, and sharing of resources efficiently via resource allocation and communication. | https://openstax.org/books/introduction-computer-science/pages/6-summary |
An OS manages computer resources (hardware) and provides services for computer programs (software). | https://openstax.org/books/introduction-computer-science/pages/6-summary |
An OS is a complex system and executes many kinds of activities ranging from executing usersâ programs, to running background jobs or scripts, to completing system programs. | https://openstax.org/books/introduction-computer-science/pages/6-summary |
Processing involves a program, a process, and a processor. An OS is responsible for managing processes, and different OSs approach process management in different ways. | https://openstax.org/books/introduction-computer-science/pages/6-summary |
The address space is the set of addresses generated by programs as they reference instructions and data. The memory space holds the actual main memory locations that are directly addressable for processing. | https://openstax.org/books/introduction-computer-science/pages/6-summary |
Computer memory consists of two main types: primary and secondary memory. An OS manages memory space through memory allocation and memory deallocation as well as by maintaining mappings from virtual addresses to physical and switching CPU context among addresses spaces. | https://openstax.org/books/introduction-computer-science/pages/6-summary |
Device drivers are the routines that interact directly with specific device types and related hardware to indicate how to initialize the device, request I/O, and handle interrupts or errors. | https://openstax.org/books/introduction-computer-science/pages/6-summary |
A device register is the interface a device presents to a programmer, whereas each I/O device appears in the physical address space of the machine as a few words. | https://openstax.org/books/introduction-computer-science/pages/6-summary |
In an OS, it is important to have dual mode operations to ensure a high level of security and authority. The dual mode is responsible for separating the user from the kernel mode. | https://openstax.org/books/introduction-computer-science/pages/6-summary |
Successful OS designs have had a variety of architectures, such as monolithic, layered, microkernels, and virtual machine monitors. As the design of an OSâand even its roleâare still evolving, it is simply impossible today to pick one âcorrectâ way to structure an OS. | https://openstax.org/books/introduction-computer-science/pages/6-summary |
A monolithic OS design is an OS architecture where the entire OS is working in kernel space. | https://openstax.org/books/introduction-computer-science/pages/6-summary |
A layered OS architecture consists of implementing the OS as a set of layers where each layer exposes an enhanced virtual machine to the layer above. | https://openstax.org/books/introduction-computer-science/pages/6-summary |
Hardware abstraction layer (HAL) is an example of layering in modern OSs. It allows an OS to interact with a hardware device at a general or abstract level rather than going deep into a detailed hardware level, which improves readability. | https://openstax.org/books/introduction-computer-science/pages/6-summary |
In a microkernel OS architecture, the functionality and capabilities are added to a minimal core OS. | https://openstax.org/books/introduction-computer-science/pages/6-summary |
Concurrent processing is a computing model that improves performance when multiple processors are executing instructions simultaneously. | https://openstax.org/books/introduction-computer-science/pages/6-summary |
A process consists of at least an address space, a CPU state, and a set of OS resources. | https://openstax.org/books/introduction-computer-science/pages/6-summary |
The OSâs process namespace particulars depend on the specific OS, but in general, the name of a process is called a PID (process ID), which is a set of unique numbers that identify processes. | https://openstax.org/books/introduction-computer-science/pages/6-summary |
The OS maintains a data structure to keep track of a process state, which is called the process control block (PCB) or process descriptor. | https://openstax.org/books/introduction-computer-science/pages/6-summary |
Concurrency refers to multiple activities and processes happening at the same time. An OS can achieve concurrent processing via the use of threads or one of three different processing environments: multiprogramming, multiprocessing, or distributed processing. | https://openstax.org/books/introduction-computer-science/pages/6-summary |
Scheduling is the act of determining which process is in the ready state and should be moved to the running state when more resources are requested than can be granted immediately, and in which order the requests should be serviced. | https://openstax.org/books/introduction-computer-science/pages/6-summary |
A good scheduling algorithm minimizes response time, efficiently utilizes resources, and implements fairness by distributing CPU cycles equitably. Four simple scheduling algorithms are FCFS, RR, STCF, and SRPT. | https://openstax.org/books/introduction-computer-science/pages/6-summary |
Synchronization is a way of coordinating multiple concurrent activities that use a shared state. | https://openstax.org/books/introduction-computer-science/pages/6-summary |
Allocation is a 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. There are three main forms of allocation: contiguous allocation, linked allocation, and index... | https://openstax.org/books/introduction-computer-science/pages/6-summary |
The OS loads executable files into memory, allows several different processes to share memory, and provides facilities for processes to exceed the memory size after they have started running. | https://openstax.org/books/introduction-computer-science/pages/6-summary |
Memory multiplexing is dividing the capacity of the communication channel into multiple logical channels. | https://openstax.org/books/introduction-computer-science/pages/6-summary |
There are several concepts that are critical to memory multiplexing, namely, isolation, sharing, virtualization, and utilization. | https://openstax.org/books/introduction-computer-science/pages/6-summary |
Time slicing is a time frame for each process to run in a preemptive multitasking CPU such that each process will be run every single time slice. | https://openstax.org/books/introduction-computer-science/pages/6-summary |
Sharing means that multiple processes can share the same piece of data concurrently. | https://openstax.org/books/introduction-computer-science/pages/6-summary |
Memory sharing improves the performance of the system because the data is not copied from one address space to another, so memory allocation is done only once. | https://openstax.org/books/introduction-computer-science/pages/6-summary |
Virtualization is a technique that gives an application the impression that it has its own logical memory and that it is independent from the available physical memory. | https://openstax.org/books/introduction-computer-science/pages/6-summary |
Fragmentation is a problem where the memory blocks cannot be allocated to the processes due to their small individual size and the distribution of sizes in the pool; there might be enough total free memory to satisfy the demand, but the available chunks cannot be allocated contiguously. | https://openstax.org/books/introduction-computer-science/pages/6-summary |
Linkers combine many separate pieces of a program, reorganize storage allocation so that all the pieces can fit together, and touch up addresses so that the program can run under the new memory organization. | https://openstax.org/books/introduction-computer-science/pages/6-summary |
There are two basic operations used in dynamic storage management to manage a memory or storage to satisfy various needs: allocate a block with a given number of bytes or free a previously allocated block. | https://openstax.org/books/introduction-computer-science/pages/6-summary |
Virtual memory is a key component of the operating system for ensuring process isolation by guaranteeing that each process gets its own view of the memory. | https://openstax.org/books/introduction-computer-science/pages/6-summary |
A file system is responsible for defining file names, storing files on a storage device, and retrieving files from a storage device. | https://openstax.org/books/introduction-computer-science/pages/6-summary |
File systems define operations on objects such as create, read, and write, and they may also provide higher-level services, such as accounting and quotas, incremental backup indexing or search, file versioning, and encryption. | https://openstax.org/books/introduction-computer-science/pages/6-summary |
File systems are concerned with lower-level characteristics such as performance and failure resilience. | https://openstax.org/books/introduction-computer-science/pages/6-summary |
The file system interface defines standard operations such the creation and deletion of files (or directories), manipulation of files and directories, copy, and lock. | https://openstax.org/books/introduction-computer-science/pages/6-summary |
File systems are responsible for managing parts of the disk that are used (inodes) and parts of the disk that are not used (free blocks). | https://openstax.org/books/introduction-computer-science/pages/6-summary |
A distributed file system (DFS) is a file system that is distributed on multiple file servers or multiple locations that support network-wide sharing of files and devices. | https://openstax.org/books/introduction-computer-science/pages/6-summary |
A DFS provides an abstraction over physical disks that is akin to the abstraction that virtual memory provides over physical memory. | https://openstax.org/books/introduction-computer-science/pages/6-summary |
We consider an OS to be reliable if it delivers service without errors or interruptions. | https://openstax.org/books/introduction-computer-science/pages/6-summary |
Protection is a general mechanism used throughout the OS and for all resources needed to be protected such as memory, processes, files, devices, CPU time, and network bandwidth. | https://openstax.org/books/introduction-computer-science/pages/6-summary |
There are three aspects to a protection mechanism: authentication, authorization, and access enforcement. | https://openstax.org/books/introduction-computer-science/pages/6-summary |
The traditional way of authentication involves a password, which is a secret piece of information used to establish the identity of a user and should be relatively long and hard to guess. Another form of authentication is two-factor authentication, which involves two factors: the system calls or texts a userâs phone ... | https://openstax.org/books/introduction-computer-science/pages/6-summary |
The authorization determines the relationship between principals, operations, and objects by defining which principals can perform which operations on which objects. | https://openstax.org/books/introduction-computer-science/pages/6-summary |
An access control list (ACL) is a list of rules that specifies which users are granted access to a specific object or resource. | https://openstax.org/books/introduction-computer-science/pages/6-summary |
A capability list is a list of objects and operations for each user that defines the user rights and capabilities. | https://openstax.org/books/introduction-computer-science/pages/6-summary |
To support access enforcement, one part of the OS must be responsible for enforcing access controls and protecting authentication and authorization information. | https://openstax.org/books/introduction-computer-science/pages/6-summary |
There are many advantages to using logging: recovery is much faster; it eliminates inconsistencies; a log can be localized in one area of disk, which makes log writes faster; and it results in better performance. One of the disadvantages of logging is that synchronous disk write happens before every metadata operation. | https://openstax.org/books/introduction-computer-science/pages/6-summary |
Virtual machines have become a fundamental component of cloud computing, as they allow cloud providers to offer scalable and flexible computing resources to users on a pay-as-you-go basis. | https://openstax.org/books/introduction-computer-science/pages/6-summary |
abstract method : declared without a code block for implementation; the stubs of methods that will be implemented by a class which uses the interface | https://openstax.org/books/introduction-computer-science/pages/7-key-terms |
abstraction : way of thinking and expressing algorithms to indicate what the programmer wants the hardware to do | https://openstax.org/books/introduction-computer-science/pages/7-key-terms |
access modifier : keyword that denotes where in code to access a variable or method | https://openstax.org/books/introduction-computer-science/pages/7-key-terms |
argument : value of a function call, which must match the parameters in both number and data type | https://openstax.org/books/introduction-computer-science/pages/7-key-terms |
array : named variable that references a block of contiguous memory locations | https://openstax.org/books/introduction-computer-science/pages/7-key-terms |
array initializer : values separated by commas placed between curly braces | https://openstax.org/books/introduction-computer-science/pages/7-key-terms |
assembly : process of converting a low-level assembly language product of the compiler into machine language that the computer can execute; binary form | https://openstax.org/books/introduction-computer-science/pages/7-key-terms |
assignment statement : operation by which a value is stored in a variable | https://openstax.org/books/introduction-computer-science/pages/7-key-terms |
back end : compiler step that is responsible for code generation or production of the target code | https://openstax.org/books/introduction-computer-science/pages/7-key-terms |
basic block : minimal-length sequence of instructions that will always execute in its entirety if it executes at all, equivalent to a code block | https://openstax.org/books/introduction-computer-science/pages/7-key-terms |
best practice : most accepted style and structure of code that can be used to ensure proper software development, which makes it possible to learn new languages easily once a programmer has mastered a given one | https://openstax.org/books/introduction-computer-science/pages/7-key-terms |
binary operator : operator surrounded by two operands | https://openstax.org/books/introduction-computer-science/pages/7-key-terms |
Boolean : data types that can hold the values true or false | https://openstax.org/books/introduction-computer-science/pages/7-key-terms |
bottom-tested loop : condition for further loop iteration set at the exit from the code block | https://openstax.org/books/introduction-computer-science/pages/7-key-terms |
busy waiting : condition of a process that is continually looking to see if it has access to a critical section, taking processor time from all processes | https://openstax.org/books/introduction-computer-science/pages/7-key-terms |
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