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This question came up today and I couldn't find any historical answer as to why a database is always represented as a cylinder. I am hoping someone in the stack world would know why and have a link or something backing it up.

Rodney S. Foley
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    http://answers.google.com/answers/threadview/id/365076.html#comments – Justin Niessner May 12 '10 at 20:50
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    @Justin Niessner: you should really post this as an answer (with the picture on this page included: http://www.cedmagic.com/history/ibm-305-ramac.html) – ChristopheD May 12 '10 at 20:52
  • I would guess it has something to do with the discs (cylinders) in a HDD. Normally it is like 3 discs in the icon which is equal to the number of disc in most HDD. The DB is stored on the HDD and I guess it is the simplest correlation as the DB is used for storing data in chunks/rows in a similar way as files are stored on the HDD. However, I do not have anything to support this theory. – alexteg May 12 '10 at 20:53

5 Answers5

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I'm reasonably certain that it predates disk drives, and goes back to a considerably older technology: drum memory:

Drum Memory

Another possibility (or maybe the choice was based on both) is a still older technology: mercury tank memory:

Mercury tank

You may have seen the symbol oriented horizontally instead of vertically, but horizontal drums were common as well:

Multiple horizontal drums

Jerry Coffin
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    Based on some of my own additional research this is the best and most plausible answer. The first databases appear to have used storage drums which where giant cylinders and it is very likely that when they represented them on paper diagrams they would use a cylinder to be the database. – Rodney S. Foley May 12 '10 at 21:19
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    I'm not enough of an expert on the history of computing to know if this answer truly is accurate, though I believe this is correct, but in any case +1 for the cool pictures of long-gone technology! – DarenW Sep 21 '10 at 17:27
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    That thing probably held about 8KB. – Alan B Jul 02 '12 at 12:21
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    Someone needs to update this! no more pictures!! – Aaron Hall May 30 '14 at 20:31
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    @AaronHall: Thanks for letting me know. Hopefully taken care of now. – Jerry Coffin May 30 '14 at 20:36
  • This is a cool answer, but if this is the case, why is a database often represented by 3 discs stacked in a cylinder? – Jason Kelley May 10 '17 at 18:08
  • @Loophole: I haven't seen that--but it would probably be a modification to make it look at least somewhat more like a disk (but that's definitely not the traditional flowchart symbol). – Jerry Coffin May 10 '17 at 18:24
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    @JerryCoffin, ever since I discovered this thread months ago, I've been stuck pondering part of your answer. *"Given that the DB symbol is normally horizontal"*, are you sure you don't mean vertical (like a stack of coins)? I have not yet once seen a db symbol represented in a horizontal fashion. I've only seen them represented in a vertical fashion. If you do mean horizontal, could you please link to even one single referenced icon that shows a db as a stack of horizontal cylinders? Thank you. – jungledev May 11 '17 at 18:17
  • @jungledev: I think there are too many sources to try to get a meaningful "vote", but at least a few [explicitly delineate between disk and drum memory](http://www.csci.csusb.edu/dick/cs372/a3FlowchartSymbols.png). – Jerry Coffin May 11 '17 at 21:49
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    Ok, now I'm way more confused @JerryCoffin. Is it possible that you meant one, but wrote the other? Sorry to be such a bother, but your references to drums and disks and horizontal and vertical just don't line up for me. Img1 vertical in image, you described to be horizontal, labeled drum. Img2. horizontal in image, you described to be vertical, labeled tank. Img3 horizontal in image, described to be vertical, labeled drum. Link in your recent comment: drum = horizontal. disk = vertical. I consider vertical as in a stack of quarters, and horizontal like a rolling pin. – jungledev May 12 '17 at 02:21
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    P.S. I am commenting rather than proposing edits to your post because I want to check with you if I'm missing something or if you might have left out some information. I don't want to simply assume that I'm right and you're wrong. – jungledev May 12 '17 at 02:23
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    @JerryCoffin just google "database symbol" and most of the first results are 3 discs stacked on top of each other, not just a cylinder. For example: https://image.freepik.com/free-icon/add-database-symbol_318-9200.jpg Surely you've seen this. I always assumed that the flow chart symbol was just a simplification of this to make it easier to draw. – Jason Kelley May 19 '17 at 14:43
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    Every database symbol I've seen is oriented like the first drum memory picture you show, not like the mercury memory. Loophole and @jungledev seem to agree. – T.C. Proctor Aug 27 '19 at 16:46
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You asked for more pics. I took these at the computer history museum in Mountain View, CA in May 2016. enter image description here Description for the above image says:

UNIVAC I mercury memory tank, Remington Rand, US, 1951

For memory, the UNIVAC used seven mercury delay line tanks. Eighteen pairs of crystal transducers in each tank transmitted and received data as waves in mercury held at a constant 149°F

Gift of William Agee X976.89

enter image description here Description for the above image says:

Williams-Kilburn tube - Manchester Mark I, Manchester University, UK, ca 1950

This was the memory in the Manchester Mark I, the successor to the "Baby." It stored only 128 40-bit words. Each bit was an electric charge that created a spot of light on the face of a "TV tube."

Gift of Manchester University Computer Science Department, X67.82

jungledev
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7

It's because people view a DB as simple storage, much like a disk. And disk storage has always been represented by a cylinder due to, well, the physical properties of spinning magnetic disks.

Matt Rogish
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It comes from the olden days (pre 1960) when data was analog, i.e. round. Nowadays with digital (square) data, databases aren't cylindrical but unfortunately the convention has stuck.

Matt Curtis
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    If analog = round and digital = square why are magnetic (digital) hard drive platers round and old analog computers giant rectangles? http://www.buzzvines.com/files/images/western_digital_green_2tb_HHD.jpg http://xpda.com/junkmail/junk162/GPN-2000-000354.jpg – Rodney S. Foley May 12 '10 at 21:28
  • @Creepy Gnome: awesome counter, but I bet they're 'shopped by digital revisionists :D – Matt Curtis May 12 '10 at 21:30
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    +1 to balance the people who did not understand the Calvin and Hobbes "The world was in black and white before the 50's" style reference. (You see it is a color picture of a black and white world.) – Ukko May 12 '10 at 22:04
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    Square data? You obviously haven't moved to the cloud yet. – Tom Anderson Apr 09 '12 at 21:02
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    This joke is too serious! – Memming Jan 06 '15 at 17:28
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I always assumed it stood for the round edges of a hard drive platter. The average consumer might not have necessarily known what a Physical Hard Drive Component looked like, so it was represented as a cylinder.

jungledev
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user3285800
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