Unit prefix

[1] In addition to those listed in the everyday-use table, the SI includes standardised prefixes for 1015 (peta), 1018 (exa), 1021 (zetta), 1024 (yotta), 1027 (ronna), and 1030 (quetta); and for 10−15 (femto), 10−18 (atto), 10−21 (zepto), 10−24 (yocto), 10−27 (ronto), and 10−30 (quecto).

For example, a 500-gigabyte hard drive holds 500 billion bytes, and a 100-megabit-per-second Ethernet connection transfers data at 100 million bits per second.

Before the adoption of ronna and quetta for 1027 and 1030 and ronto and quecto for 10−27 and 10−30 in November 2022, many personal, and sometimes facetious, proposals for additional metric prefixes were formulated.

[14][15][16][17][18] In 2010, an online petition sought to establish hella- as the SI prefix for 1027, a movement that began on the campus of UC Davis.

[19][20] The prefix, which has since appeared in the San Francisco Chronicle, Daily Telegraph, Wired and some other scientific magazines, was recognised by Google, in a non-serious fashion, in May 2010.

They were changed because of previously proposed ascending hepto (Greek "hepta" (7)) was already in use as a numerical prefix (implying seven) and the letter "h" as both SI-accepted non-SI unit (hour) and prefix (hecto 102), the same applied to "s" from previously proposed descending septo (i.e. SI unit "s", seconds), while "o" for octo was problematic since a symbol "o" could be confused with zero.

Using Greek for ascending and Latin for descending would be consistent with established prefixes such as deca, hecto, kilo vs. deci, centi, milli.

[26] In 2001, a few unofficial prefixes appeared on the Internet: hepa (1021), ento (10−21), otta (1024), fito (10−24), nea (1027), syto (10−27), dea (1030), tredo (10−30), una (1033) and revo (10−33).

The Oxford professor Jeffrey K. Aronson has suggested extending beyond zetta/zepto and yotta/yocto with xenta/xenno, wekta/weko, vendeka/vendeko, and udeka/udeko, based on the idea that the "Z" and "Y" prefixes would continue backwards through the English alphabet.

He goes on to list a large number of prefixes, starting with Xona, Weka, Vunda, Uda, Treda, Sorta, ... Another proposal for xenta/xona is novetta, from the Italian "nove" (or "nine").

In 1993, Morgan Burke proposed, as a joke, harpo for 10−27, groucho for 10−30 (and therefore harpi for 1027, grouchi for 1030, zeppi for 1033, gummi for 1036, and chici for 1039), all of these being references to the comedy act, the Marx Brothers.

Distance marker on the Rhine : 36 (XXXVI) myriametres from Basel