I am trying to burn an ISO image to a DVD.

The DVD is supposed to store 4.7 GB, but when I try to burn the image to it, Windows says the DVD is too small. The image is 4.51 GB big, and uses 4.51 GB on disk.

Why won’t Windows let me burn the image to disc?


DVDs can store 4.7 GB of data according to commu^H^H^H^H^Hhard drive manufacturer propaganda. In reality, they can store about 4700 million bytes, which is only ~4.3 GB.

  • 1
    More specifically, Storage makers use 'SI' units where kilo is 1000, while programmers use binary units where kilo is 1024, which make more sense when working with binary
    – Journeyman Geek
    Mar 10 '13 at 11:31
  • What's the difference between GB and GiB then?
    – osvein
    Mar 10 '13 at 11:58
  • 1
    1 KiB is 1024 bytes, 1 KB is 1000 bytes. 1 GiB is 1024x1024x1024 bytes (1073741824 bytes), 1 GB us 1000000000 bytes.
    – Hennes
    Mar 10 '13 at 14:23
  • 1
    Aye. I prefer the power of two terms. But the XiB terms also makes sense since it keeps things nicely consistent. That way K is always 1000, M is always 1000000, not just 'everywhere except ...'. It takes some getting used to when we grew up with the 'real numbers' and when they are so much more convenient.
    – Hennes
    Mar 10 '13 at 14:40
  • 2
    Using binary prefixes to report file sizes is a bad habit Microsoft taught us. Mac OS X and Ubuntu both use decimal prefixes. Their applications either use decimal prefixes or the proper IEC binary prefixes (e.g., K3b and Deluge on Ubuntu how KiB, MiB, etc.). Binary prefixes make sense for RAM size (always a power of two), but the capacities of hard drives, DVDs and Blu-ray Discs, the speeds of PCIe, SATA and Internet and Ethernet connections, as well as the frequency of CPUs etc. are always reported using decimal prefixes.
    – Dennis
    Mar 16 '13 at 16:48

Windows displays file size incorrectly. The image reported to be 4,51 GB in size is actually 4,51 GiB (gibibytes), which is approximately 4,82 GB.

In 'SI units', we use a factor 1000 for prefixes, because that's a round number in the decimal system. 1000 equals 1 kilo, 1000 kilo equals 1 mega and so on. In the binary system, the closest round number is 1024. However confusing to someone not very familiar with binary numbers, 1024 was often used as a base for the sake of simplicity. To signify the difference between a normal and a 'binary' kilobyte, a common convention was to use a capital K for the latter (i.e. 1 KB = 1024 B = 1,024 kB).

As symbols for the prefixes mega-, giga- etc. were already capitalised, an alternate scheme was proposed that included an 'i' after the symbol: 1 KiB = 1024 B, 1 MiB = 1024 KiB... Unfortunately, the convention of the so-called kibibyte was far less universally adopted, resulting in possible ambiguity. Often, numbers a presented with SI units, whether 1000 or 1024 has been used as a base internally. As a result, a hard drive manufacturer's gigabyte can be roughly 7% smaller than your operating system's gigabyte.

In your case, the image really is too large to fit on the dvd, but both sizes are displayed using different conventions.

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  • 2
    @kinokijuf: The practice of representing 1024 bytes as exactly one kilobyte isn't nearly as long-established as the metric system which has been used for centuries and whose kilo in turn is derived from the ancient Greek word for 'thousand', which predates the use of 'kilobyte' by kiloyears. Mar 10 '13 at 16:49
  • Byte isn’t a SI unit.
    – kinokijuf
    Mar 10 '13 at 19:57

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