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Semaphore (lit. ' apparatus for signalling '; from Ancient Greek σῆμα (sêma) 'mark, sign, token' and Greek -φόρος (-phóros) 'bearer, carrier') [1] is the use of an apparatus to create a visual signal transmitted over distance. [2] [3] A semaphore can be performed with devices including: fire, lights, flags, sunlight, and moving arms.
Semaphores are signalling mechanisms which can allow one or more threads/processors to access a section. A Semaphore has a flag which has a certain fixed value associated with it and each time a thread wishes to access the section, it decrements the flag. Similarly, when the thread leaves the section, the flag is incremented.
Optical communication, also known as optical telecommunication, is communication at a distance using light to carry information. It can be performed visually or by using electronic devices . The earliest basic forms of optical communication date back several millennia, while the earliest electrical device created to do so was the photophone ...
In the 1790s, the first fixed semaphore systems emerged in Europe. However, it was not until the 1830s that electrical telecommunication systems started to appear. This article details the history of telecommunication and the individuals who helped make telecommunication systems what they are today.
The operators would move the semaphore arms to successive positions to spell out text messages in semaphore code, and the people in the next tower would read them. An optical telegraph is a line of stations, typically towers, for the purpose of conveying textual information by means of visual signals (a form of optical communication ).
A system like flag semaphore, with an alphabetic code, can certainly send any given message, but the system is designed for short-range communication between two persons. An engine order telegraph , used to send instructions from the bridge of a ship to the engine room, fails to meet both criteria; it has a limited distance and very simple ...
In computer science, interprocess communication (IPC) is the sharing of data between running processes in a computer system. Mechanisms for IPC may be provided by an operating system . Applications which use IPC are often categorized as clients and servers , where the client requests data and the server responds to client requests. [ 1 ]
German semaphore home signals, which are totally different in appearance to the British semaphore signal, include one or two white arms with a red outline and a small circular disk at the end of it, and coloured lenses which display the position of the aspect(s) of the signal during nighttime operation and these arms face right of the post.