OS X eats up cd/dvd capacity

B

Bauer

Registered
My IT Dept wont give us a burn applic so we have to use the OS to archive onto cd/dvd. Why does the OS take so much room to do its voodoo. On a cd of 700 MB there is only 640 MB available and on a DVD only 4.27 GB of 4.7 GB is burnable.
 
Hey Bauer

Which version of osx are you using because this doesnt seem to be the case for me? I just burnt a 694 MB file via finder in 10.4.4 and ive never had any problems getting the maximum capacity of a dvdr
 
Technically, 700MB CD-Rs are a "hack." They use sections of the disk that the standard dictates they really shouldn't to try and fit more data on the CD, and are usually referred to as "non-standard":

A standard CD-R is a 1.2 mm thick disc made of polycarbonate with a 120 mm or 80 mm diameter. It has a storage capacity of 74 minutes of audio or 650 MB of data. Non-standard CD-Rs are available with capacities of 79 minutes, 59 seconds and 74 frames /736,966,656 bytes (702 MB), which they achieve by slightly exceeding the tolerances specified in the Orange Book CD-R/CD-RW standards. Most CD-Rs on the market are of the latter capacity. There are also 90 minute/790 MB and 99 minute/870 MB discs, though they are rare.
Click to expand...

From: http://en.wikipedia.org/wiki/CD-R

I have found that OS X sometimes does not recognize 700MB CD-Rs and instead reports them as 640MB CD-Rs. Would it be possible to simply compress a few files, then burn the CD, to get it under the 640MB limit?
 
If the OS reads 640, that is all you will get. If the OS doesn't read beyound that limit - you cannot fudge that without an OS hack or something similar. We are talking about less than 1% of a CD.
 
There are a few issues at play, here.

As others have said, sometimes the Finder won't acknowledge the full size of a CD. I just don't use the Finder to burn CDs if I can avoid it. I use Toast, or YuBurner (free), or Firestarter FX (also free). None of them have ever given me problems, and they all let me fill every bit of that 702.8MB. If you have sufficient privileges, try downloading one of those apps.

The issue with CDs and DVDs is a little different, though. DVDs do not hold 4.7GB of data! At least not by software standards. The confusion comes from the two different definitions of KB/MB/GB. In hard drive sizes, "GB" almost always means "one billion bytes" (decimal counting). But all software defines a GB as 2^30 bytes (binary counting; that's 1,073,741,820). CDs are measured using binary counting. DVDs are not, for some annoying reason.

Therefore, a DVD's "4.7GB" = 4,700,000,000 bytes = 4.377 GB by software standards.

Another factor to consider is formatting size. The invisible HFS+ database files can be quite large on volumes with many files. I don't think that could account for the ~100MB of missing space you're getting on your DVD, though.
 
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