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Operating-system-level Virtualization
OS-level virtualization is an operating system (OS) paradigm in which the kernel allows the existence of multiple isolated user space instances, called ''containers'' ( LXC, Solaris containers, Docker, Podman), ''zones'' (Solaris containers), ''virtual private servers'' (OpenVZ), ''partitions'', ''virtual environments'' (VEs), ''virtual kernels'' (DragonFly BSD), or ''jails'' (FreeBSD jail or chroot jail). Such instances may look like real computers from the point of view of programs running in them. A computer program running on an ordinary operating system can see all resources (connected devices, files and folders, network shares, CPU power, quantifiable hardware capabilities) of that computer. However, programs running inside of a container can only see the container's contents and devices assigned to the container. On Unix-like operating systems, this feature can be seen as an advanced implementation of the standard chroot mechanism, which changes the apparent root folder ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Operating System
An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs. Time-sharing operating systems schedule tasks for efficient use of the system and may also include accounting software for cost allocation of processor time, mass storage, printing, and other resources. For hardware functions such as input and output and memory allocation, the operating system acts as an intermediary between programs and the computer hardware, although the application code is usually executed directly by the hardware and frequently makes system calls to an OS function or is interrupted by it. Operating systems are found on many devices that contain a computer from cellular phones and video game consoles to web servers and supercomputers. The dominant general-purpose personal computer operating system is Microsoft Windows with a market share of around 74.99%. macOS by Apple Inc. is in second place (14.84%), and ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Virtual Machine
In computing, a virtual machine (VM) is the virtualization/emulation of a computer system. Virtual machines are based on computer architectures and provide functionality of a physical computer. Their implementations may involve specialized hardware, software, or a combination. Virtual machines differ and are organized by their function, shown here: * '' System virtual machines'' (also termed full virtualization VMs) provide a substitute for a real machine. They provide functionality needed to execute entire operating systems. A hypervisor uses native execution to share and manage hardware, allowing for multiple environments which are isolated from one another, yet exist on the same physical machine. Modern hypervisors use hardware-assisted virtualization, virtualization-specific hardware, primarily from the host CPUs. * Process virtual machines are designed to execute computer programs in a platform-independent environment. Some virtual machine emulators, such as QEMU and video ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
QEMU
QEMU is a free and open-source emulator (Quick EMUlator). It emulates the machine's processor through dynamic binary translation and provides a set of different hardware and device models for the machine, enabling it to run a variety of guest operating systems. It can interoperate with Kernel-based Virtual Machine (KVM) to run virtual machines at near-native speed. QEMU can also do emulation for user-level processes, allowing applications compiled for one architecture to run on another. Licensing QEMU was written by Fabrice Bellard and is free software, mainly licensed under the GNU General Public License (GPL for short). Various parts are released under the BSD license, GNU Lesser General Public License (LGPL) or other GPL-compatible licenses. Operating modes QEMU has multiple operating modes: ;User-mode emulation: In this mode QEMU runs single Linux or Darwin/macOS programs that were compiled for a different instruction set. System calls are thunked for endianness and for ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
VMware ESXi
VMware ESXi (formerly ESX) is an enterprise-class, type-1 hypervisor developed by VMware for deploying and serving virtual computers. As a type-1 hypervisor, ESXi is not a software application that is installed on an operating system (OS); instead, it includes and integrates vital OS components, such as a kernel. After version 4.1 (released in 2010), VMware renamed ESX to ''ESXi''. ESXi replaces Service Console (a rudimentary operating system) with a more closely integrated OS. ESX/ESXi is the primary component in the VMware Infrastructure software suite. The name ''ESX'' originated as an abbreviation of Elastic Sky X. In September 2004, the replacement for ESX was internally called ''VMvisor'', but later changed to ESXi (as the "i" in ESXi stood for "integrated"). Architecture ESX runs on bare metal (without running an operating system) unlike other VMware products. It includes its own kernel. In the historic VMware ESX, a Linux kernel was started first and then used to ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Emulator
In computing, an emulator is Computer hardware, hardware or software that enables one computer system (called the ''host'') to behave like another computer system (called the ''guest''). An emulator typically enables the host system to run software or use peripheral devices designed for the guest system. Emulation refers to the ability of a computer program in an electronic device to emulate (or imitate) another program or device. Many Printer (computing), printers, for example, are designed to emulate Hewlett-Packard, HP LaserJet printers because so much software is written for HP printers. If a non-HP printer emulates an HP printer, any software written for a real HP printer will also run in the non-HP printer emulation and produce equivalent printing. Since at least the 1990s, many video game enthusiasts and hobbyists have used emulators to play classic arcade games from the 1980s using the games' original 1980s machine code and data, which is interpreted by a current-era s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
System Call
In computing, a system call (commonly abbreviated to syscall) is the programmatic way in which a computer program requests a service from the operating system on which it is executed. This may include hardware-related services (for example, accessing a hard disk drive or accessing the device's camera), creation and execution of new processes, and communication with integral kernel services such as process scheduling. System calls provide an essential interface between a process and the operating system. In most systems, system calls can only be made from userspace processes, while in some systems, OS/360 and successors for example, privileged system code also issues system calls. Privileges The architecture of most modern processors, with the exception of some embedded systems, involves a security model. For example, the ''rings'' model specifies multiple privilege levels under which software may be executed: a program is usually limited to its own address space so that ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Full Virtualization
In computer science, virtualization is a modern technique developed in late 1990s and is different from simulation and emulation. Virtualization employs techniques used to create instances of an environment, as opposed to simulation, which models the environment; or emulation, which replicates the target environment such as certain kinds of virtual machine environments. Full virtualization requires that every salient feature of the hardware be reflected into one of several virtual machines – including the full instruction set, input/output operations, interrupts, memory access, and whatever other elements are used by the software that runs on the bare machine, and that is intended to run in a virtual machine. In such an environment, any software capable of execution on the raw hardware can be run in the virtual machine and, in particular, any operating systems. The obvious test of full virtualization is whether an operating system intended for stand-alone use can successful ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Live Migration
Live migration refers to the process of moving a running virtual machine (VM) or application between different physical machines without disconnecting the client or application. Memory, storage, and network connectivity of the virtual machine are transferred from the original guest machine to the destination. The time between stopping the VM or application on the source and resuming it on destination is called 'downtime'. When the downtime of a VM during live migration is small enough that it is not noticeable by the end user, it is called a 'seamless' live migration. Live migration of Virtual Machines Two techniques for moving the virtual machine's memory state from the source to the destination are pre-copy memory migration and post-copy memory migration. Pre-copy memory migration Pre-copy phase In pre-copy phase, the Hypervisor copies all the memory pages from source to destination while the VM is still running on the source. If some memory pages change (become 'dirty') d ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Application Virtualization
Application virtualization is a software technology that encapsulates computer programs from the underlying operating system on which they are executed. A fully virtualized application is not installed in the traditional sense, although it is still executed as if it were. The application behaves at runtime like it is directly interfacing with the original operating system and all the resources managed by it, but can be isolated or sandboxed to varying degrees. In this context, the term "virtualization" refers to the artifact being encapsulated (application), which is quite different from its meaning in hardware virtualization, where it refers to the artifact being abstracted (physical hardware). Description Full application virtualization requires a virtualization layer. Application virtualization layers replace part of the runtime environment normally provided by the operating system. The layer intercepts all disk operations of virtualized applications and transparently redirec ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
User Account
A user is a person who utilizes a computer or network service. A user often has a user account and is identified to the system by a username (or user name). Other terms for username include login name, screenname (or screen name), account name, nickname (or nick) and handle, which is derived from the identical citizens band radio term. Some software products provide services to other systems and have no direct end users. End user End users are the ultimate human users (also referred to as operators) of a software product. The end user stands in contrast to users who support or maintain the product such as sysops, database administrators and computer technicians. The term is used to abstract and distinguish those who only use the software from the developers of the system, who enhance the software for end users. In user-centered design, it also distinguishes the software operator from the client who pays for its development and other stakeholders who may not directly us ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Webcam
A webcam is a video camera which is designed to record or stream to a computer or computer network. They are primarily used in videotelephony, livestreaming and social media, and security. Webcams can be built-in computer hardware or peripheral devices, and are commonly connected to a device using USB or wireless protocols. Webcams have been used on the Internet as early as 1993, and the first widespread commercial one became available in 1994. Early webcam usage on the Internet was primarily limited to stationary shots streamed to web sites. In the late 1990s and early 2000s, instant messaging clients added support for webcams, increasing their popularity in video conferencing. Computer manufacturers also started integrating webcams into laptop hardware. In 2020, the COVID-19 pandemic caused a shortage of webcams due to the increased number of people working from home. History Early development (early 1990s) First developed in 1991, a webcam was pointed at the Trojan ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Computer Peripheral
A peripheral or peripheral device is an auxiliary device used to put information into and get information out of a computer. The term ''peripheral device'' refers to all hardware components that are attached to a computer and are controlled by the computer system, but they are not the core components of the computer, such as the CPU or power supply unit. In other words, peripherals can also be defined as devices that can be easily removed and plugged into a computer system. Several categories of peripheral devices may be identified, based on their relationship with the computer: *An ''input device'' sends data or instructions to the computer, such as a mouse, keyboard, graphics tablet, image scanner, barcode reader, game controller, light pen, light gun, microphone and webcam; *An ''output device'' provides output data from the computer, such as a computer monitor, projector, printer, headphones and computer speaker; *An ''input/output device'' performs both input and output func ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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