# What's the exact size of a zettabyte?

Is a zettabyte 1021 bytes or 270 bytes?

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Love the way that the main SU questions list page can't cope with superscripts, so I was doing a 'WTF' at the question "Is a zettabyte 1021 bytes or 270 bytes?" –  Linker3000 Oct 12 '11 at 19:52
A zettabyte is more than you can afford. 8-)} –  Keith Thompson Oct 12 '11 at 21:35
8-)} is supposed to mean? –  Pacerier Oct 12 '11 at 21:42

While is true that the theory goes as wikipedia says (1ZB=10^21 and 1ZiB=2^70), the truth is that "it depends".

Storage devices basic unit is not the byte, but sectors, which until recently (for compatibility) were always 512 bytes.

That means that a 64MB USB disk (as an example) will probably have the number of sectors to be greater than 1MB (SI), but will never be exactly that because of the basic unit being 512 bytes. This device will probably have 64*1000*512*2 bytes = 64KB * 1KiB = 65536000 bytes, which is not 64MB (64000000 bytes), nor 64MiB (67108864 bytes).

The same for normal hard disks, but their basic unit is usually greater than a single sector, although always a multiple of it.

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I'm wondering how wikipedia get that GiB ZiB MiB info. or did they invented that –  Pacerier Oct 12 '11 at 21:43
The Kibibyte (KiB) unit was "invented" by the IEC in 1999 as a way to stop the confusion between computer scientists and the "rest of the world". For computer scientists, 99.99% (made up percentage) of all interesting numbers are a power of 2, so 2^10 (KiB), 2^20 (MiB), etc. But the rest of the world works with base 10 in mind, and those units don't make sense. –  nlucas Oct 12 '11 at 22:20
if you can find a credible source for the claim above i'll mark this as answer =D –  Pacerier Oct 13 '11 at 1:04
en.wikipedia.org/wiki/Kibibyte –  nlucas Oct 13 '11 at 10:46

A zettabyte are 1021 bytes = 1.000.000.000.000.000.000.000 Byte

270 bytes are called Zebibyte.

To quote from Wikipedia:

There has been considerable confusion about the meanings of SI (or metric) prefixes used with the unit byte, especially concerning prefixes such as kilo (k or K) and mega (M) as shown in the chart Prefixes for bit and byte. Since computer memory is designed with binary logic, multiples are expressed in powers of 2, rather than 10. The software and computer industries often use binary estimates of the SI-prefixed quantities, while producers of computer storage devices prefer the SI values.

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Now this is where it is weird. Google says it gives 1 GB storage instead of 1 GiB storage, but when we count the bytes it goes to 2^30 instead of 10^9 –  Pacerier Oct 12 '11 at 18:42
I had these backwards and had to look it up. physics.nist.gov/cuu/Units/binary.html –  Rob Oct 12 '11 at 18:44
Pacerier: From Wikipedia: There has been considerable confusion about the meanings of SI (or metric) prefixes used with the unit byte, especially concerning prefixes such as kilo (k or K) and mega (M) as shown in the chart Prefixes for bit and byte. Since computer memory is designed with binary logic, multiples are expressed in powers of 2, rather than 10. The software and computer industries often use binary estimates of the SI-prefixed quantities, while producers of computer storage devices prefer the SI values. –  RoflcoptrException Oct 12 '11 at 18:49
SI is the way to go, roflcoptr. D: If one were to pick up a zettabyte drive, It may be either 10^20 or 2^70, depending on the manufacturer. –  Rob Oct 12 '11 at 18:55
Cool, you'd may wanna add that to the answer –  Pacerier Oct 12 '11 at 18:58