Re: silug: Azureus and Mozilla downloads bigger than normal? --

["Bryan J. Smith" <b.j.smith@ieee.org>]

On Sun, 2005-01-02 at 08:37, bentley.rhodes wrote:
> hi there.  i was using Mozilla's download manager and noticed that when
> i download the ISO files for FC3, 2, or whatever (mainly ISO's) they are
> bigger than what they are supposed to be.  For instance, the fC3 and FC2
> cd's were half a gig or more larger than what they were supposed to be.
> so if they were supposed to be 4.02 gigs, they were 4.3 to 4.5 gigs when
> they claimed to be finished.  They were still downloading too at that
> point.  Same thing is happening with Azureus.

Welcome to the great Prefix debate!

In a nutshell, people have long debated whether standard, 3 placeholder
metrix prefixes should be multiples of 1,000 (10^3) or 1,024 (2^10) for
binary.

For the most part, multiples of 1,024 were accepted for many years. 
This differs from other metric prefixes which are 1,000.  But the
significance wasn't noticable in the days of Kilobytes.

But with each higher prefix, the different is _exponential_.
  Kilo:  2.4%
  Mega:  2.4^2 =  5.8%
  Giga:  2.4^3 = 13.8%
  Tera:  2.4^4 = 33.2%

Yes, literally 1/3rd at 10^12 Terabyte v. 2^40 Terabyte!

E.g., Manufacturers then started inflating their numbers by using 1,000
instead of 1,024.  Because a 40GB is actually only 40*10^9/2^30 or
37.2GB.

In your case, it's the opposite.  4.02 * 2^30/10^9 = 4.316!

That's why various international organizations sought to address this. 
More directly, the IEEE Computer Society finally standardized on a new
nomenclature -- IEEE 1541.

First off, the standard ISO metric prefixes _stay_ as multiples of 1,000
for each 3 places.  This is for consistency.  So in your case, your DVD
images are 4.316GB, not 4.02GB.

Secondly, a new "Binary" prefix is introduced in IEEE 1541.  From long
to abbreviated to suffix, this is:  

  2^10 = Kilobinary = Kibi = Ki ... 1 KiB = 1.024 KB
  2^20 = Megabinary = Mebi = Mi ... 1 MiB ~ 1.058 MB
  2^30 = Gigabinary = Gibi = Gi ... 1 GiB ~ 1.138 GB
  2^40 = Terabinary = Tebi = Ti ... 1 TiB ~ 1.332 TB

A lot of people complain this "breaks" the traditional association of
1,024 to 3 places, but in reality, there is some consistency needed. 
There are some initial assumptions and problems, yes, but the sooner we
have a consistent output format, the better.

So if you see MiB next time in a listing or other size reference, don't
think the developer is just a fan of the movies.  ;->  It just means the
developers are aware of IEEE 1541, and they are using the proper
nomenclature to state "yes, this is a Megabinary 2^20, not possibly a
Mega 10^6."

The binary prefixes are recommended, since it is not ambiguous if
someone uses the traditional metric prefixes, which are still commonly
used for both.


-- 
Bryan J. Smith                                    b.j.smith@ieee.org 
-------------------------------------------------------------------- 
Subtotal Cost of Ownership (SCO) for Windows being less than Linux
Total Cost of Ownership (TCO) assumes experts for the former, costly
retraining for the latter, omitted "software assurance" costs in 
compatible desktop OS/apps for the former, no free/legacy reuse for
latter, and no basic security, patch or downtime comparison at all.




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