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I'm curious why a chunk of binary data is called image?

Like disk image, boot image, Linux image, flash image, etc.

In my brain, image is something two-dimensional, but binary data is a one-dimensional octet flow.

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closed as general reference by simchona, kiamlaluno, StoneyB, Daniel, Mahnax Sep 27 '12 at 3:22

This question is too basic; it can be definitively and permanently answered by a single link to a standard internet reference source designed specifically to find that type of information.If this question can be reworded to fit the rules in the help center, please edit the question.

up vote 6 down vote accepted

Usage like this of image dates from the early years of computing, when "IBM cards" were in common use. For example, RFC 678 (19 December 1974) devotes a paragraph to defining Card Image, which Wikipedia refers to as "an archaic term for an ASCII string, usually 80 bytes in length." Card image is used similarly in pdf CDC document 60137400 pdf (January 1966), but in current usage now often refers to SD memory-card images.

The rationale behind such usage is to express the notion of "as-is" or "true" copy. For example, binary image or executable image often refer to previously-translated and linked code that could be loaded into memory as-is and executed. The ngrams below shows growth and decline in usage of several image terms. (Note that much of the usage of binary image charted below is for digital representation of pictures, vs. usage discussed above.) ngram

Ngrams also shows that in the last 15 years, usage of disk image has become more common than the corresponding boot, CD, and executable terms. Wikipedia remarks: "A disk image is usually created by creating a complete sector-by-sector copy of the source medium and thereby perfectly replicating the structure and contents of a storage device" (which agrees with the "as-is" or "true-copy" concept mentioned earlier).

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