In "Getting Things Done", David Allen refers to "Open Loops", meaning things that are incomplete.

Q: What past reference to an "Open loop" is he alluding to? Is that phrase "Open Loop" something that's been used in other areas before and is being redefined by David Allen, or is this a brand new phrase?

  • 2
    I believe an open loop is a line ;) Apr 4, 2011 at 15:18
  • 12 more characters to go before I can post "lol". Apr 7, 2011 at 18:59

3 Answers 3


Informal definitions here: In any system, results (output) which influence further actions (input) constitute a "Closed Loop". If the results of actions do not directly influence further input, you have an "Open Loop".

Strictly speaking, an open loop is no loop at all. In a closed loop system, the output "loops back" and in some way effects the input.

Common examples: Cruise control on a vehicle is a closed loop - changes to load, etc, are 'fed back' into the control system to effect how much the vehicle must accelerate or decelerate to maintain a relatively constant speed.

If you pay no attention to what effect your marketing has on your sales, and make no changes to it based on that, you have an "Open Loop".

These phrases have been around at least since the dawn of computer science. I don't know "Getting things done", but in most cases a closed loop would certainly be part of effective management.

  • 2
    +1; To add to this, an analogy of an open or closed loop is that of an open or closed circuit.
    – MrHen
    Apr 4, 2011 at 15:45
  • 1
    @MrHen I expected that as the first answer here. (Not that there's anything wrong with the others.... )
    – jbelacqua
    Apr 4, 2011 at 22:38

See open-loop controller and open-loop model.

Both involve systems in which direct results cannot be observed by the controlling system or the player of a game.


In my experience, it is slang used by electronics savvy people for someone having a total mental breakdown over an event or issue. "Man he went open loop! He was screaming, throwing stuff around his office..." With the obvious parallel to a control circuit in a system losing it's feed back loop. =)

  • "parallel to a circuit" ;-)
    – Jack Ryan
    Dec 23, 2013 at 17:18

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