# How much does \[electronic\] data weigh?

**URL:** <https://boards.straightdope.com/t/how-much-does-electronic-data-weigh/561418>\
**Category:** Factual Questions\
**Created:** [November 21, 2010, 6:51am UTC](https://boards.straightdope.com/t/how-much-does-electronic-data-weigh/561418 "2010-11-21T06:51:38Z")\
**Posts on this page:** 3\
**Page:** 3

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**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\
**Post date:** [October 31, 2011, 4:33pm UTC](https://boards.straightdope.com/t/how-much-does-electronic-data-weigh/561418/41 "2011-10-31T16:33:38Z")

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> [@Half\_Man\_Half\_Wit](#):
>
> Where does that number come from? The minimum energy needed to erase a bit is kTln(2) Joule, where k is Boltzman’s constant and T is the temperature, about 2.9 \* 10[sup]-21[/sup] J in numbers, equal to a mass of 3.2 \* 10[sup]-38[/sup] kg, if I did the numbers right.

Can you orient me about what you’re talking about?

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**Author:** ![Half\_Man\_Half\_Wit](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/half_man_half_wit/32/21766_2.png) [@Half\_Man\_Half\_Wit](https://boards.straightdope.com/u/Half_Man_Half_Wit)\
**Post date:** [October 31, 2011, 5:18pm UTC](https://boards.straightdope.com/t/how-much-does-electronic-data-weigh/561418/42 "2011-10-31T17:18:04Z")

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> [@Leo\_Bloom](#):
>
> Can you orient me about what you’re talking about?

[Landauer’s principle](http://en.wikipedia.org/wiki/Landauer%27s_principle). The gist of it is, thermodynamic entropy and information are related; under just the right circumstances, one bit of information corresponds to kln(2) J/K entropy. In particular, erasing a bit on some computing device incurs an entropy increase of minimally this amount. This corresponds to an energy change of kTln(2) J.

(An earlier thought experiment by Leo Szilard, known as ‘Szilard’s engine’, arrived at the same relationship between energy and information: Maxwell’s demon, in the case where he watches over a box in which there is only one single molecule moving linearly, needs one bit of information – which half of the box the particle is in – to extract useful energy of just kTln(2) Joule: if the particle is in the left half of the box, he closes a shutter between the two halves, then slides a piston into the right half, and opens the shutter again; the particle, ‘expanding’ isothermally, does then work by pushing out the piston again, to which you then could attach a (tiny) load. This experiment has (in a modified form) actually been [performed recently](http://arxiv.org/abs/1009.5287).)

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**Author:** ![Leo\_Bloom](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leo_bloom/32/10377_2.png) [@Leo\_Bloom](https://boards.straightdope.com/u/Leo_Bloom)\
**Post date:** [November 1, 2011, 5:19am UTC](https://boards.straightdope.com/t/how-much-does-electronic-data-weigh/561418/43 "2011-11-01T05:19:42Z")

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> [@Half\_Man\_Half\_Wit](#):
>
> [Landauer’s principle](http://en.wikipedia.org/wiki/Landauer%27s_principle). The gist of it is, thermodynamic entropy and information are related; under just the right circumstances, one bit of information corresponds to kln(2) J/K entropy. In particular, erasing a bit on some computing device incurs an entropy increase of minimally this amount. This corresponds to an energy change of kTln(2) J.

Effing great stuff. I followed the Wik to [Entropy in thermodynamics and information theory - Wikipedia](http://en.wikipedia.org/wiki/Entropy_in_thermodynamics_and_information_theory) and was like a pig in mud. Thanks.

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