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Feedback, arrangement for the automatic self-regulation of an electrical, mechanical, or biological system by returning part of its output as input. A simple example of feedback is provided by a governor on an engine; if the speed of the engine exceeds a preset limit, the governor reduces the supply of fuel, thus decreasing the speed. Electronic control systems employ feedback extensively. In voltage and current regulators, part of the output is used as a control input, providing self-regulation. For example, if the output becomes too great, it acts through the feedback loop to reduce itself. The use of feedback as the fundamental control mechanism for machinery occurs in automation. Living organisms possess feedback control systems of great complexity. For example, when the hand reaches for an object, information about its position is continuously fed back to the brain, both by the eyes and by position-sensing nerves in the arm; the brain uses the position information to guide the hand to the object. Such feedback can be termed voluntary, since it is to some extent under conscious control. Automatic, involuntary feedback is constantly taking place as well, controlling processes such as respiration, circulation, digestion, and maintenance of body temperature. Feedback is one of the main concerns of cybernetics. See control systems. See also biofeedback.

Positive feedback Positive feedback is a type of feedback. Open systems (ecological, biological, social) contain many types of regulatory systems, among which are systems that involve positive feedback and its relative negative feedback. When a change of variable occurs in a system, the system responds. In the case of positive feedback the response of the system is to change that variable even more in the same direction. For a simple example, imagine an ecosystem with only one species and an unlimited amount of food. The population will grow at a rate proportional to the current population, which leads to positive feedback. This has a de-stabilizing effect, so left unchecked, does not result in homeostasis. In some cases (if not controlled by negative feedback), a positive feedback loop can run out of control, and can result in the collapse of the system. Positive and negative do not mean or imply desirability. The negative feedback loop tends to slow down a process, while the positive feedback loop tends to speed it up. Positive feedback is used in certain situations where rapid change is desirable. One common example of positive feedback is the network effect, where more people are encouraged to join a network the larger that network becomes. The result is that the network grows more and more quickly over time. In electrical engineering Feedback is well understood and widely studied in electrical engineering. Whereas negative feedback is used to stabilize the response of an electrical system and reduce nonlinear effects, positive feedback is often used to take advantage of these nonlinear effects (for example, the Schmitt trigger), or at least is used with the understanding that nonlinear effects, not feedback, will limit the output (in oscillators, and in popular configurations for MESFET amplifiers). An important consideration in the design of feedback amplifiers is to avoid unintentionally creating positive feedback (see frequency compensation). Positive feedback from loudspeakers to a microphone causes the familiar squealing sound.

In gaming In games, positive feedback is a critical and heavily exploited mechanism for controlling the resources in a game. It has a number of uses: To speed up a game that would otherwise be too slow. For example, if the annual income did not increase in SimCity as the city grew, it would take many years to earn enough money to fill the large map with structures. To create a feeling of growth and progress. For example, in a role-playing game, it's typical for players to struggle with enemies near the beginning that later become easy to destroy due to enhanced strength and weapons, purchased with the experience and gold earned by those early encounters. To magnify small advantages. For example, in Starcraft, a player who has more resources will be able to build more units, enabling them to seize more resource-rich territory and so gain yet more resources. This allows a player with a small resource advantage to crush their opponent in time. However, accidental positive feedback loops in games can also be a source of degenerate strategies, destroying the game's challenge. For example, suppose a player in a first-person shooter gained 100 health points for every person they killed. Then, a careful player could quickly amass a large number of health points and become virtually indestructible.

Guest book A guestbook, in the context of an Internet website, is a logging system that allows visitors to that website to indicate their thoughts about the site or its subject. Normally, it does not require creation of a user account, as it is normally an informal method of dropping off a quick note. The purpose of a website guestbook is normally to display the kind of visitors the site gets, including the part of the world they reside in, presented as a linear list of messages. It is normally not intended for purposes of carrying on discussions. A guestbook is, therefore, different from a chat room (which is more or less realtime communication), or an internet forum (which is sectioned out in subject threads).