how big is the cd image

[Iberê Fernandes]

On Thu, May 10, 2012 at 6:38 PM, Jonathan Marsden <jmarsden at fastmail.fm>wrote:

> Paul,
>
> On Thu, May 10, 2012, at 08:14 PM, paul sutton wrote:
>
> > According to ubuntu  the cd image is 721.7 MB (721,727,488 bytes) in
> > size according to windows it is 688mb (721,727,488 bytes) in size
> > (well a recorded cd is that size)
> >
> > So which one of these is correct, given that the image needs to fit on
> > a normal 700mb cd-r otherwise it needs a dvd
>
> Both are "correct" -- they just use different definitions of "MB"!
>
> Ubuntu is using the ISO and disk manufacturer standard that 1MB =
> 1000000 bytes.  Windows is (I think) using the "computer industry"
> definition of the "binary MB", which ISO calls a "MibiByte", in which
> 1MB (or 1MiB per ISO) = 2^10 = 1024 * 1024 = 1048576 bytes.
>
> The image is under 700 "computer industry" (binary) MB, so it will fit
> on a CD-R blank.
>
> In case you care, the official Ubuntu policy on units is documented at
>
>  https://wiki.ubuntu.com/UnitsPolicy
>
> To verify the size of a CD-R blank, in Ubuntu or Lubuntu you can install
> wodim by doing
>
>  sudo apt-get install wodim
>
> and then put your CD-R blank in the drive, and do
>
>  wodim -atip |grep "lead out"
>
> The number right after the : in the output line, outside of any
> parentheses, is the number of 2048 byte allocation units available on
> the CD-R.  On one I just tested here, it output
>
>  ATIP start of lead out: 359846 (79:59/71)
>
> so the number of clusters is 359846, which means the total bytes
> available to write data to on that CD-R blank is given by
>
>  echo $((359846 * 2048))
>
> which outputs 736964608, which is larger than the size in bytes of the
> CD image you mentioned, which was 721727488.
>
> Bottom line: it fits, don't worry so much :)
>
> Jonathan
> --
>  Jonathan Marsden
>  jmarsden at fastmail.fm



Jonathan, wow... thank you  for the detailed reply. I like to learn a bit
everyday!

Cheers,
Ibere
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