I do not find that answer convincing. Both drum memory (<a href="https://en.wikipedia.org/wiki/Drum_memory" rel="nofollow">https://en.wikipedia.org/wiki/Drum_memory</a>) and mercury delay line memory (<a href="https://en.wikipedia.org/wiki/Delay-line_memory#Mercury_delay_lines" rel="nofollow">https://en.wikipedia.org/wiki/Delay-line_memory#Mercury_dela...</a>) were used as primary memory, not for storage.<p>In addition mercury delay lines lost their data when unpowered.<p>My money would be on <a href="https://en.wikipedia.org/wiki/Disk_pack" rel="nofollow">https://en.wikipedia.org/wiki/Disk_pack</a>. Those are objects that people carried around to move data (<a href="http://www.catb.org/esr/writings/taoup/html/ch02s01.html" rel="nofollow">http://www.catb.org/esr/writings/taoup/html/ch02s01.html</a>: <i>Ken Thompson quietly began answering requests by shipping out tapes and disk packs — each, according to legend, with a note signed “love, ken”</i>)<p>Call it the floppy disk of the 1970s
> Why is a database always represented with a cylinder?<p>Because that's the data bucket. At least that's what I learned at university. Seriously.