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Polling (computer Science)
Polling, or interrogation, refers to actively sampling the status of an external device by a client program as a synchronous activity. Polling is most often used in terms of input/output (), and is also referred to as polled or software-driven . A good example of hardware implementation is a watchdog timer. Description Polling is the process where the computer or controlling device waits for an external device to check for its readiness or state, often with low-level hardware. For example, when a printer is connected via a parallel port, the computer waits until the printer has received the next character. These processes can be as minute as only reading one bit. This is sometimes used synonymously with ' busy-wait' polling. In this situation, when an operation is required, the computer does nothing other than check the status of the device until it is ready, at which point the device is accessed. In other words, the computer waits until the device is ready. Polling also ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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External Device
A peripheral device, or simply peripheral, is an auxiliary hardware device that a computer uses to transfer information externally. A peripheral is a hardware component that is accessible to and controlled by a computer but is not a core component of the computer. A peripheral can be categorized based on the direction in which information flows relative to the computer: * The computer receives data from an ''input device''; examples: mouse, keyboard, scanner, game controller, microphone and webcam * The computer sends data to an ''output device''; examples: monitor, printer, headphones, and speakers * The computer sends and receives data via an ''input/output device''; examples: storage device (such as disk drive, solid-state drive, USB flash drive, memory card and tape drive), modem, router, gateway and network adapter Many modern electronic devices, such as Internet-enabled digital watches, video game consoles, smartphones, and tablet computers, have interfaces ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Signal (IPC)
Signals are standardized messages sent to a running program to trigger specific behavior, such as quitting or error handling. They are a limited form of inter-process communication (IPC), typically used in Unix, Unix-like, and other POSIX-compliant operating systems. A signal is an asynchronous notification sent to a process or to a specific thread within the same process to notify it of an event. Common uses of signals are to interrupt, suspend, terminate or kill a process. Signals originated in 1970s Bell Labs Unix and were later specified in the POSIX standard. When a signal is sent, the operating system interrupts the target process's normal flow of execution to deliver the signal. Execution can be interrupted during any non-atomic instruction. If the process has previously registered a signal handler, that routine is executed. Otherwise, the default signal handler is executed. Embedded programs may find signals useful for inter-process communications, as sign ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Kqueue
Kqueue is a scalable event notification interface introduced in FreeBSD 4.1 in July 2000, also supported in NetBSD, OpenBSD, DragonFly BSD, and macOS. Kqueue was originally authored in 2000 by Jonathan Lemon, then involved with the FreeBSD Core Team. Kqueue makes it possible for software like nginx to solve the c10k problem. The term "kqueue" refers to its function as a "kernel event queue" Kqueue provides efficient input and output event pipelines between the kernel and userland. Thus, it is possible to modify event filters as well as receive pending events while using only a single system call to kevent(2) per main event loop iteration. This contrasts with older traditional polling system calls such as poll(2) and select(2) which are less efficient, especially when polling for events on numerous file descriptors. Kqueue not only handles file descriptor events but is also used for various other notifications such as file modification monitoring, signals, asynchronous I ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Integer (computer Science)
In computer science, an integer is a datum of integral data type, a data type that represents some interval (mathematics), range of mathematical integers. Integral data types may be of different sizes and may or may not be allowed to contain negative values. Integers are commonly represented in a computer as a group of binary digits (bits). The size of the grouping varies so the set of integer sizes available varies between different types of computers. Computer hardware nearly always provides a way to represent a processor word size, register or memory address as an integer. Value and representation The ''value'' of an item with an integral type is the mathematical integer that it corresponds to. Integral types may be ''unsigned'' (capable of representing only non-negative integers) or ''signed'' (capable of representing negative integers as well). An integer value is typically specified in the source code of a program as a sequence of digits optionally prefixed with + or −. S ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Interrupt Request (PC Architecture)
In a computer, an interrupt request (or IRQ) is a hardware signal sent to the processor that temporarily stops a running program and allows a special program, an interrupt handler, to run instead. Hardware interrupts are used to handle events such as receiving data from a modem or network card, key presses, or mouse movements. Interrupt lines are often identified by an index with the format of ''IRQ'' followed by a number. For example, on the Intel 8259 family of programmable interrupt controllers (PICs) there are eight interrupt inputs commonly referred to as ''IRQ0'' through ''IRQ7''. In x86 based computer systems that use two of these Programmable Interrupt Controller, PICs, the combined set of lines are referred to as ''IRQ0'' through ''IRQ15''. Technically these lines are named ''IR0'' through ''IR7'', and the lines on the Industry Standard Architecture, ISA bus to which they were historically attached are named ''IRQ0'' through ''IRQ15'' (although historically as the numbe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Infinite Loop
In computer programming, an infinite loop (or endless loop) is a sequence of instructions that, as written, will continue endlessly, unless an external intervention occurs, such as turning off power via a switch or pulling a plug. It may be intentional. There is no general algorithm to determine whether a computer program contains an infinite loop or not; this is the halting problem. Overview This differs from "a type of computer program that runs the same instructions continuously until it is either stopped or interrupted". Consider the following pseudocode: how_many = 0 while is_there_more_data() do how_many = how_many + 1 end display "the number of items counted = " how_many ''The same instructions'' were run ''continuously until it was stopped or interrupted'' . . . by the ''FALSE'' returned at some point by the function ''is_there_more_data''. By contrast, the following loop will not end by itself: birds = 1 fish = 2 while birds + fish > 1 do birds = 3 - bird ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Bit Banging
Bit banging is a term of art that describes a method of digital data transmission as using general-purpose input/output (GPIO) instead of computer hardware that is intended specifically for data communication. Controlling software is responsible for satisfying protocol requirements including timing which can be challenging due to limited host system resources and competing demands on the software. In contrast, dedicated communication hardware (e.g., UART, SPI, I²C) satisfies protocol requirements which tends to reduce the runtime load on the controlling system software and its host processor. In particular, some communication hardware provides data buffering to lower the runtime load of the controlling system. The bit banging method may allow a computer to support a protocol with limited or no hardware changes and therefore bit banging can be a lower cost option since changing software is typically less expensive than changing hardware. Bit banging is commonly used ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Asynchronous I/O
In computer science, asynchronous I/O (also non-sequential I/O) is a form of input/output processing that permits other processing to continue before the I/O operation has finished. A name used for asynchronous I/O in the Windows API is '' overlapped I/O''. Input and output (I/O) operations on a computer can be extremely slow compared to the processing of data. An I/O device can incorporate mechanical devices that must physically move, such as a hard drive seeking a track to read or write; this is often orders of magnitude slower than the switching of electric current. For example, during a disk operation that takes ten milliseconds to perform, a processor that is clocked at one gigahertz The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), often described as being equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose formal expression in terms of SI base un ... could have performed ten million instruct ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Abstraction (computer Science)
In software engineering and computer science, abstraction is the process of generalizing concrete details, such as attributes, away from the study of objects and systems to focus attention on details of greater importance. Abstraction is a fundamental concept in computer science and software engineering, especially within the object-oriented programming paradigm. Examples of this include: * the usage of abstract data types to separate usage from working representations of data within programs; * the concept of functions or subroutines which represent a specific way of implementing control flow; * the process of reorganizing common behavior from groups of non-abstract classes into abstract classes using inheritance and sub-classes, as seen in object-oriented programming languages. Rationale Computing mostly operates independently of the concrete world. The hardware implements a model of computation that is interchangeable with others. The software is structured in archit ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Ethernet Hub
An Ethernet hub, active hub, network hub, repeater hub, multiport repeater, or simply hub is a network hardware device for connecting multiple Ethernet devices together and making them act as a single network segment. It has multiple input/output (I/O) ports, in which a signal introduced at the input of any Computer port (hardware), port appears at the output of every port except the original incoming. A hub works at the physical layer. A repeater hub also participates in collision detection, forwarding a jam signal to all ports if it detects a collision (telecommunications), collision. In addition to standard 8P8C ("RJ45") ports, some hubs may also come with a BNC connector, BNC or an Attachment Unit Interface (AUI) connector to allow connection to legacy 10BASE2 or 10BASE5 network segments. Hubs are now largely obsolete, having been replaced by network switches except in very old installations or #Uses, specialized applications. As of 2011, connecting network segments by repe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Network Switch
A network switch (also called switching hub, bridging hub, Ethernet switch, and, by the IEEE, MAC bridge) is networking hardware that connects devices on a computer network by using packet switching to receive and forward data to the destination device. A network switch is a multiport network bridge that uses MAC addresses to forward data at the data link layer (layer 2) of the OSI model. Some switches can also forward data at the network layer (layer 3) by additionally incorporating routing functionality. Such switches are commonly known as layer-3 switches or multilayer switches. Switches for Ethernet are the most common form of network switch. The first MAC Bridge was invented in 1983 by Mark Kempf, an engineer in the Networking Advanced Development group of Digital Equipment Corporation. The first 2 port Bridge product (LANBridge 100) was introduced by that company shortly after. The company subsequently produced multi-port switches for both Ethernet and FDDI such as ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Star Network
A star network is an implementation of a spoke–hub distribution paradigm in computer networks. In a star network, every host is connected to a central hub. In its simplest form, one central hub acts as a conduit to transmit messages. The star network is one of the most common computer network topologies. Network The hub and hosts, and the transmission lines between them, form a graph with the topology of a star. Data on a star network passes through the hub before continuing to its destination. The hub manages and controls all functions of the network. It also acts as a repeater for the data flow. In a typical network the hub can be a network switch, Ethernet hub, wireless access point or a router The star topology reduces the impact of a transmission line failure by independently connecting each host to the hub. Each host may thus communicate with all others by transmitting to, and receiving from, the hub. The failure of a transmission line linking any host to the h ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |