what is the etymology of `loop device`

Question

What is the etymology of the term loop device

score 2 · Accepted Answer · answered Jul 06 '14 at 05:15

I believe it is from loopback,

Loopback, or loop-back, refers to the routing of electronic signals, digital data streams, or flows of items back to their source without intentional processing or modification.

It is a loop device because it is backed by a file on a different file-system.

See also Loopback Device,

A Loopback Device is a mechanism used to interpret files as real devices. The main advantage of this method is that all tools used on real disks can be used with a loopback device.

Good enough. I would have named it differently. – H2ONaCl Jul 07 '14 at 14:52 — H2ONaCl, Jul 07 '14 at 14:52

score 1 · Answer 2 · answered Jul 06 '14 at 05:15

I have no proof of this but I always took the term "loop device" to be drawn from the musical reference "loop".

Looping Music today typically employs tape delay/feedback systems, digital delay devices, or computers to create repetitions of sounds. These repetitions can either remain limited to simple repeated phrases, or they are allowed to add up to a complex sound texture which either stands for itself or is used as an atmospheric or rhythmic background for soloing or other musical expression.

Source: http://www.loopers-delight.com/history/Loophist.html

Also the Wikipedia page on music loops.

"A loop is a sample of a performance that has been edited to repeat seamlessly when the audio file is played end to end" (Hawkins 2004, p. 10).

Anything that can be fed back onto itself in some manner is a "loop", and is often the case with "loop devices", one is often mounting the contents of a file that's present on the current filesystem blown out as a pseudo directory structure within that same filesystem.

Your last paragraph explains it well I think. The music reference is unnecessary as it rather creates a loop with the definition... ;) — The Quark, Jan 20 '22 at 12:26

score 0 · Answer 3 · answered Mar 14 '20 at 16:15

I remember it the following way.

Imagine there is an external device, which replicates the data in your iso file. Insert it and mount it. The result will be the same as if you have run mount -o loop iso_image ...

Thus, when performing mount -o loop iso_image ..., a loop is formed in a sense: root device -> (refers to) -> imaginary external device replicating the iso image -> (refers back to) -> root device (because the iso image is stored physically on the root device).

what is the etymology of `loop device`

3 Answers3