Re: Units of measure

<On 13 Nov 98, at 12:29, Matthew Atkinson wrote: > > A Terabyte (with only 1 'r') is 1024 GB, or 2^40 bytes > A Petabyte is 1024TB, or 2^50 bytes > An Exabyte (without the 'h') is 1024PB, or 2^60 bytes > Just for interest, and perhaps for the future (!?) a Zettabyte > is 1024EB or 2^70 bytes, and a Yottabyte is 1024ZB or 2^80 bytes. <and a tad later Billy Wheeler replied: > How can a Zettabyte come before a Yottabyte? :-) <at this point I thought I'd stick my oar in and add: > Actually, to be really pedantic, units start with lower-case letters: kilobyte, megabyte, gigabyte, right up to yottabyte. The prefix _symbols_ from mega- onward (not kilo-) have capital letters: k, M, G, up to Y. And a measure is written with a space between the magnitude and the unit: thus 1024 Gbyte, 1024 Pbyte etc. These prefixes and conventions are maintained by the BIPM (International Bureau of Weights and Measures) in Sevres, France, after having been adopted at an about-five-yearly CGPM (General Conference of...). The byte is not an official BIPM unit so doesn't have an official international symbol. I suppose kB and so on are harmless enough, though I prefer kbyte when I'm in pedantic mood. (It's Friday afternoon and I've spent all week on a single Y2K parallel run, so I like to relax with irrelevant pedantry.) (And obviously, they all follow the computing approximation that 2^10 = 1000.) I was violently ill when I first read about zetta and yotta and still feel the stomach heave when I think of them. The corresponding submultiple prefixes are just as bad, zepto- (symbol z) for 10^(-21) and yocto- (symbol y) for 10^(-24). The thinking behind them is this. Mega, giga, and tera come from the Greek for big, giant, and monster respectively. They were enough for a few years. Then when they wanted some bigger ones, they found the sequence "giant, monster..." wasn't easily continuable. So they reanalysed tera as if from tetra- "four" (mega = 1000^2, giga = 1000^3, tera=1000^4). This suggested the idea of bending some more Greek numbers. So they coined peta- and exa- by arbitrary deformation of penta- and hexa-. But peta and exa look nice. Recently they wanted even more and applied the same principle but with much uglier deformation of Latin: zepto- and zetta- from sept-, yocto- and yotta- from oct-. They must have seen that sticking the y- in after a z- looked weird, but this CGPM was obviously on drugs of some kind, so they decided it was cool, doesn't matter, we can hack that. My apologies for wasting your bandwidth. --- Nicholas Widdows [The opinions in this are mine only, not those of Trace PLC. Mine make more sense, for one thing. A geek code is available on request.]