why does the file fit in the cd?

Posted on 2004-10-28
Last Modified: 2010-04-03
Hi, could someone please tell me why a .iso or .bin image file bigger than 700mb can fit on a 700mb cd? I am really does it work?
Question by:wakemeup
    LVL 95

    Accepted Solution

    Certain filesystem overhead is not needed for certain types of files/CDs
    LVL 95

    Expert Comment

    by:Lee W, MVP
    Or it could be error correction - see here:

    Expert Comment

    When examing files its important to remember that 1 kilobyte = 2 ^ 10 byes, or 1024 bytes.  Often this causes certain issues when trying to see file size in Windows.  To avoid this, check the properties of the file, this number is always more precise.

    In terms of why an .iso or a .bin fits on a cd when its greater than 700 mb, there is some overhead in these files.  Also there is overhead in the file system itself, (NTFS, FAT32) that isn't necesary in CDFS.  (Examples: Bitmaps (NTFS) and File Allocation Tables (FAT)).  
    LVL 3

    Assisted Solution

    A CD image file, such as an .ISO or .bin is actually a hard drive image of data and a file system, ISO9660, CDFS, or something similar.  Depending on how the image was made, it may or may not contain many file system structures which don't count in the 700 MB of "user data" a 700 MB holds.  So, a 700 MB CD actually holds more than 700 MB, but it will only hold slightly more than 700 MB of actual user data.  You can get about 40 MB more on a CD with overburn, available in some CD burning programs.  
    LVL 2

    Expert Comment

    but can't overburn ruin cd/cd burner and then not be readable in the other drive though? i burned a cd and it was like 2 megs over so i didnt think over burn could do any damage, but then it wouldnt read in my cd player-- it was all jumbled... this might belong in another question :p but still.

    Expert Comment

    The reason is happens is because as SuperCableMan says, it doesnt exactly equal 700MB.

    The CD supports upto 700MB, BUT 99% of cd's are larger than this margenally, and have the capability to "overburn" which basically puts a larger image on a cd.

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