How Many Yottabytes in a Quettabyte? Extreme Numbers Get New Names

How Many Yottabytes in a Quettabyte? Extreme Numbers Get New Names

By the 2030s, the world will generate around a yottabyte of data per year–that’s 1024 bytes, or the amount that would fit on DVDs stacked all the way to Mars. The data sphere’s explosive growth has prompted the governors to agree on new prefixes to describe the large and small.

Representatives from governments worldwide, meeting at the General Conference on Weights and Measures (CGPM) outside Paris on 18 November, voted to introduce four new prefixes to the International System of Units (SI) with immediate effect. The prefixes ronna and quetta represent 1027 and 1030, and ronto and quecto signify 10-27 and 10-30. Earth is approximately one ronnagram in weight, and an electron’s total mass is one quectogram.

This is the first update to the prefix system since 1991, when the organization added zetta (1021), zepto (10-21), yotta (1024) and yocto (10-24). In that case, metrologists were adapting to fit the needs of chemists, who wanted a way to express SI units on the scale of Avogadro’s number–the 6 x 1023 units in a mole, a measure of the quantity of substances. The more familiar prefixes peta and exa were added in 1975 (see ‘Extreme figures’).

Extreme Figures table

Today’s driver is data science, says Richard Brown (a metrologist at UK National Physical Laboratory in Teddington). He has been working on plans to introduce the latest prefixes for five years, and presented the proposal to the CGPM on 17 November. With the annual volume of data generated globally having already hit zettabytes, informal suggestions for 1027–including ‘hella’ and ‘bronto’–were starting to take hold, he says. Google’s unit converter, for example, already tells users that 1,000 yottabytes is 1 hellabyte, and at least one UK government website quotes brontobyte as the correct term.

” “From a metrology perspective, this sort of horrified my, because these are completely informal terms,” Brown says. He says that in the past, SI has adopted unofficial terms. But the problem with hella and bronto is that their symbols (h and b) are already used in the metric system for other units or prefixes: h, for example, stands for hecto (the rarely used 102) and H is the henry, the unit of inductance. He says this is the main reason they don’t work as formal terms. He smiles and adds, “It’s not that I wanted to killjoy, but that comes into it as also.”

Prefix precedents

It was difficult to come up with new prefixes. Brown searched for words that started with letters that were not used as symbols for units and prefixes or excluded from use–r, R, q, and Q. The names were derived from the use of precedents for the most recent prefixes. Prefixes that describe the smaller end of a scale, such atto, or multiply figures such as giga, are referred to as ‘o’. Another was that the words should roughly correspond with the sounds of Greek or Latin numbers (ronna and quetta sound a bit like the Greek words for nine and ten, ennea and deka). Brown had to drop the earlier suggestion of “quecca” after realizing its proximity to a Portuguese swearword.

The resulting prefixes were “very thoughtful” and the product of years of discussion, says Georgette McDonald, director-general at Canada’s Metrology Resource Centre in Halifax. She says that they are consistent and avoid confusion.

The SI doesn’t need new prefixes to represent large numbers at the moment, she says, but it makes sense to introduce terms for the smaller scale. “We don’t know if we’re measuring anything at this scale. She says it is better to have the scale balanced, and the prefixes related to each other in a consistent way.

Quetta and Ronna might sound strange now but giga and Tera were once, says Olivier Pellegrino a metrologist at Portugal’s Institute of Quality in Caparica. He says they will feel normal with practice.

Brown says that there are now no letters of the alphabet available to represent new prefixes, so what will happen once some area of science pushes magnitudes to the 1033 level remains an open question. Brown says that scientists can always denote numbers in powers ten but people prefer a word. Brown would prefer compound prefixes that use two symbols (such as kiloquetta, kQ), over branching into different alphabets. He adds, “But I think we’re a long ways away from having to worry about that.”

Brown had to go through so many hoops in order to get his proposal accepted at the CPGM, he said. He can’t even imagine the terms being used. “It will absolutely be absolutely fantastic .”

This article is reproduced with permission and was first published on November 18 2022.

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