or, stuff that I dragged out of my head

Location: Moncton, New Brunswick, Canada

Wednesday, December 01, 2010


A foolish, avoidable error in a recent Farhad Manjoo column in usual suspect Slate:

I've got a 1-terrabyte USB drive that I keep connected to my main household machine, a fast Windows 7 desktop.

No, he doesn't. He's got a 1-terabyte drive.

The "tera-" in "terabyte" is Greek, as are all the prefixes for large numbers of bytes, which we will get to in a minute. Adding that extra "-r-" turns it into "terra", which is Latin for "earth" and completely unrelated to the Greek: instead, it's from the Indo-European "ters-", "dry", because the land is (self-evidently) dry as opposed to the sea. (The word "thirst" is also descended from this root.)

You know, for someone who is so devoted to computers, Manjoo doesn't seem to have much use for a spellchecker.

"Tera-" may look familiar to those with a taste for esoteric medicine, because it is also the root of the word "teratoma", literally a "monster tumor" which contains tissue such as hair or teeth. "Tera-" means "monster", and a terabyte, one thousand gigabytes, is a scarily large amount of data. Or used to be, before one-terabyte hard drives became standard equipment. (I've got one in my computer and another external backup drive connected to it.)

So here are all the big-number prefixes:

"kilo-", "one thousand", from "khiloi", with the same meaning. Also seen in "kilometre" and "kilogram".

"mega-", "one million", from "megas", "great". Also seen in "megaton" and "omega" ("big 'o'", as opposed to "omicron", "little 'o'").

"giga-", "one billion", from "gigas", "giant". Also seen in "gigantic".

"tera-", "one trillion", from "teras", "monster", as we have seen.

"peta-", "one quadrillion", derived from "penta-", "five", for the fifth big number.

"exa-", "one quintillion", derived from "hexa-", "six", for the sixth big number.

"zetta-", "one sextillion", derived from "zeta", the Greek name for (perversely) the last letter of the Roman alphabet, on the assumption that this was the last big number that would ever be needed. (Compare with the Commonwealth pronunciation of the last letter of the alphabet, "zed".)

"yotta-", "one septillion", derived from "iota", the Greek name for the second-last letter of the Latin alphabet, since "zeta" was already taken by someone who didn't think big enough.

I suppose this is also the place to point out that not every system uses the same names for big numbers such as billion and trillion. The North American system boosts the counter every three zeroes, as I have done above: billion ("bi-" for "two"), trillion ("tri-" for "three"), and so on. The British system interpolates French-derived numbers and boosts the counter every six zeroes: after million comes milliard, then billion, followed by billiard, and so on. It would probably be easier to reduce the whole thing to groups of agreed-upon terms--our billion is "one thousand million", our quadrillion "one thousand million million"--or to just use scientific notation.


Blogger D.J. said...

And, of course, there's the (proposed) next one after yotta-: hella-.

Friday, December 03, 2010 8:08:00 AM  

Post a Comment

<< Home