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When 50 MB are not 50 MB

I'm a big fan of the Inside Security Rescue CD. The CD squeezes a Linux (Debian based) with a working GUI, diagnostics and repair tools (anti virus, partition and hard disk check) on 50 MB of space. It even contains support to write CDs or DVDs. Why is 50 MB to magic? 50 MB is the storage capacity of a name card size CD-ROM. I always carry one (or a few) with me. The NTFS support is read only but seems to be more tolerant than Microsoft's own NTFS implementation. A number of times where 2000 or XP refused to recognize a NTFS partition anymore the Rescue CD could still read most of it.
The CDs are very popular. Whenever I show what you can do with it to clients or colleagues, I own one less (glad to be of service).
So I ran out of my mini CD and went to restock. This time I got Melody NameCard CD-R. The CD writer refused to write the image. I use Roxio, that doesn't tell how much short of storage you are (only that). Only the windows CD writer (which can't write ISO images) told me: 48 MB to write 47 MB free. So I had a second look:  On the package: 50 MB/5min, actual space inside: 47 MB. Am I out of luck or short changed by the manufacturer? Or is 6% less space (on all 10 of the package) within tolerance?
Update:  I got a nice reply from the manufacturer. They apologized for my inconvenience and explained: The guaranteed storage is 5 minutes of music. One minute is about 9.5 MB, so 5x9.5 = 47.5 MB. Production tolerance can lead to CDs with more capacity. The 50MB are the same marketing blah as your 200GB harddisk. However there is a 6 minute CD available, also labelled 50 MB which has enough storage.

Posted by on 12 September 2005 | Comments (1) | categories: Technology


  1. posted by icelava on Wednesday 14 September 2005 AD:
    50,000,000 bytes / 1048576 = 47.68MB

    which is why 4.7GB DVDs are in reality 4.38GB. The same despicable mathematical rule used by hard disk vendors.

    The only saving grace are the regular CDs, where 703MB _really_ is 703MB byte for byte. This was the collapsing point for me when I "upgraded" from CD-writing to DVD-writing. The very _same_ manufacturers of the CDs use _different_ formulas for the media.

    If they can _properly_ do so for CDs, _why_ can't they for DVDs? Again, despicable.