chain (redirected from pulling chain)

chain, flexible series of connected links used in various ways, especially for the transmission of motive power, for hoisting (see pulley), and for securing or fastening. Commonly, mechanical energy from a motor or other source applied to a sprocket wheel is conveyed by means of an endless chain to another sprocket wheel for driving a mechanism. Examples of such an arrangement are found in bicycles, motorcycles, and conveyor belts. The chain in this application is so designed that each consecutive link fits over a sprocket, the distance between links being called the pitch. The relative speed of the wheels varies according to their relative circumferences and, thus, the number of sprockets on each. There are several types of chain for the transmission of power. A detachable-link chain has links that are simple rectangles, each with a connecting hook at one end by which it is attached to the next link. A pintle chain has links that are approximately U-shaped. The closed end of each link fits into the open end of the next one; a pin holds the two links together. A block chain consists of metal blocks that are joined together by side plates and pins to form links. A roller chain has links consisting of side plates with hollow cylindrical rollers between them. Pins pass through the rollers and side plates to hold the links together. A silent, or inverted-tooth, chain has links made of toothed metal plates. A number of these links are placed side by side to form a group. Each group is joined to another one by meshing the ends of the links of both groups and inserting a pin there. By repeating the process a chain can be formed. Its width can be varied by varying the number of links in a group. Although not completely silent, this type of chain is quieter than other power transmission chains. The coil chains used in hoists and for locking or fastening purposes are of the open-link type, comprising solid interlocked rings, or of the stud-link type, in which a stud, or bar, across the link keeps the chain from kinking.

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1.	(operating system)	chain - (From BASIC's "CHAIN" statement) To pass control to a child or successor without going through the operating system command interpreter that invoked you. The state of the parent program is lost and there is no returning to it. Though this facility used to be common on memory-limited microcomputers and is still widely supported for backward compatibility, the jargon usage is semi-obsolescent; in particular, Unix calls this exec. Compare with the more modern "subshell".
2.	(programming)	chain - A series of linked data areas within an operating system or application program. "Chain rattling" is the process of repeatedly running through the linked data areas searching for one which is of interest. The implication is that there are many links in the chain.
3.	(theory)	chain - A possibly infinite, non-decreasing sequence of elements of some total ordering, S x0 <= x1 <= x2 ... A chain satisfies: for all x,y in S, x <= y \/ y <= x. I.e. any two elements of a chain are related. ("<=" is written in LaTeX as \sqsubseteq).