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What is the max number files allowed on a DVD?

By SNGX1275 · 4 replies
Jan 7, 2009
  1. I did some breif googling and was unable to find an answer, I may have just overlooked it. Does anyone know offhand how many can go on a dvd? I imagine it depends on how you burn it, ISO or UDF but I don't know for sure.

    This question came up when I was asked to back up an old mac hard drive so a guy could get the files off of it after a PSU failure, where it wasn't worth buying a new PSU (since the computer hadn't been used in years anyway). The hard drive was only 2 gig (yeh the Mac came from back when legal Mac clones existed) so it will fit on a single layer dvd.

    Just was wondering how many files could go on a DVD.. I'm sure its probably 10-100x the amount that were on the drive but I was curious.
  2. kimsland

    kimsland Ex-TechSpotter Posts: 14,524

    Generally, writable DVD discs come in 12cm (120 mm) and 8cm (80 mm) diameter sizes. The most commonly used is the larger 12cm type

    A (12cm) "4.7 GB" media has 4.7 * 1 000 000 = 4.700.000.000 bytes / 1024/1024/1024 = 4.377 GB

    4.7 GB disc stores 4.7 billion bytes [4:700,000,000 bytes ÷ 1000 = 4,700,000 KB ÷ 1000 = 4,700 MB ÷ 1000 = 4.7 GB]

    Note: usable space may in fact be smaller ie around 4.27GB, due to sectors and disc formatting


    Writable DVD discs can either be single (SS 4.7 GB) or double-sided (DS 9.4 GB) or double-sided double-layer ~17 GB (rare)

    The amount of information that can be written is determined by the disc’s recording capacity as well as the physical and logical formats used.

    All writable DVD formats devote the same amount of usable space to data (2,048 bytes per sector). DVD+R, DVD+RW and DVD-RAM specify the number of sectors available for user information (4.7 GB DVD+R/+RW 2,295,104 sectors, 4.7 GB DVD-RAM 2,295,072 sectors) so disc capacity can be calculated by multiplying the user data area size by the number of disc sectors. For example, a 4.7 GB DVD+R disc: 2,048 bytes/sector x 2,295,104 sectors = 4,700,372,992 bytes. This rounds to roughly 4.7 GB (decimal notation).

    DVD-R and DVD-RW, on the other hand, do not stipulate the number of sectors that are dedicated to user information but simply that a minimum capacity must be available on the disc. In the case of DVD-R (version 1.0) this is 3.95 (12 cm) and 1.23 (8 cm) billion bytes and for DVD-R (Authoring), DVD-R (General) and DVD-RW 4.7 (12 cm) and 1.46 (8 cm) billion bytes. Consequently, real world capacity can vary slightly among discs from different media manufacturers although many have informally settled on 2,298,496 sectors (4,707,319,808 bytes) for a DVD-R (General) 4.7 GB disc.

    Be aware, however, that the logical format (UDF, FAT, HFS etc.) as well as any defect management system employed consume space otherwise available for user information

    Each DVD sector contains 2418 bytes of data, 2048 bytes of which are user data. And has in total 4,700,372,992 bytes on the entire disc

    Therefore using maths (and approximating the amount of total usable data space on a DVD 4.7GB Disc)

    4,700,372,992 ÷ 2048 = approximately 2,300,000 files (but more likely around 1.5 Million due to loss of space\burning program used\type of format\ etc etc

    This information mostly (but not all) has been taken from here: http://www.osta.org/technology/dvdqa/dvdqa6.htm
    And here: http://en.wikipedia.org/wiki/DVD
    And here: http://www.google.com ;)

    Does that answer your small question?
  3. SNGX1275

    SNGX1275 TS Forces Special Topic Starter Posts: 10,729   +409

    Yep :) Thanks for the research.

    I was only copying about 6600 files, I was sure that was within the limits (as I said). Turns out the capacity was about an order of magnitude above what I thought for the high end.
  4. kimsland

    kimsland Ex-TechSpotter Posts: 14,524

    Seeming you replied, I found this unrelated info whilst searching as well
    (I'm only putting it here, because it has an indirect relevancy here!)

    Maximum number of files on an NTFS volume

    4,294,967,295 (2 to the power of 32 minus 1 file)

    There is no limit to the number of files that can be stored in a NTFS HardDrive folder
  5. jobeard

    jobeard TS Ambassador Posts: 10,432   +801

    Filesystem Comparisons

    filesystems are just wonderful :)
    The media presents the MAX(raw storage), but the filesystem controls:
    1. max(filename length)
    2. max(filesize)
    3. max(path length)
    4. max(dir nesting)
    5. and even the character set(s) allowed (ie: some don't support unicode)
    here's a reference for some tidbits (albeit not very complete)

    This description of UDF (used for all DVDs) is interesting but doesn't answer the question.

    found this:
    In most cases (1) and (3) become the same thing, causing (4) to be DERIVED (as opposed to fixed) from the sum of the dir names in the path + the filename length.

    [edit] found a real prize: Compare Filesystems [/edit]
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