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I have a Kingston SDHC card 4 GB speed class 4, but on Windows 7 it's recognized only with 3.68 GB space available.

I've already formatted the card and I get only 3.68 GB. How I can get 4 GB space available on the card?

3 Answers 3

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The reason for the discrepancy is that Kingston is labeling the card based on the base-10 value of GB, where one GB is 1000000 bytes, while Windows is reporting the card based on the base-2 value of GB (also called GiB), where one GB is 1073741824 bytes.

4 * 1000000000 / 1073741824 is equal to roughly 3.7.

The answer is that you can't get 4 GB of space available because your card physically doesn't have that much space.

You can see http://en.wikipedia.org/wiki/Gigabyte for more information.

Hard drive and storage manufacturers like to use 10^9 as the value for a GB because it lets them advertise more space. 2^30 is the actual relevant measurement.

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    It is not just hard drive mfg's who consider the "G" unit prefix to stand for 10-to-the-9th-power: it is anyone who understands what the metric prefixes mean and have been used to signify since the nineteenth century!
    – kreemoweet
    Oct 9, 2012 at 21:04
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This is common. The size of the card is advertised as 4GB where 1GB is 1,000 MB. However, that is not accurate. There are actually 1,024 MB in a full GB. Manufacturers use the "1,000" all the way through the conversion instead of the correct 1,024.

Using the proper number to calculate gigabytes should give you something like 4GB = 4,294,967,296 bytes. However, the manufacturer advertises 4GB = 4,000,000,000 bytes. 4,000,000,000 bytes is, in fact, around 3.68GB.

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  • There is nothing wrong in considering 1 GByte = 1,000,000,000 bytes. Quite the reverse, actually.
    – kreemoweet
    Oct 9, 2012 at 21:07
  • @kreemoweet is correct. Hard drives have been sold using SI prefixes (powers of 1000) since the very first hard drive (the IBM 350 RAMAC). And nearly every hard drive, memory card, etc., these days has a notation on the box or package that says "1 GB = 1,000,000,000 bytes". SI prefixes are also used for clock rates, data transfer speeds (on internal buses, USB, Ethernet, etc.), radio frequencies, etc., etc. It's mostly only RAM that's the outlier, but for some reason Microsoft chose to show both RAM and disk and file sizes using the misleading "binary" meanings of M, G, etc. Feb 9, 2017 at 5:31
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Binary/Decimal differences is one option, but I think in the case the "missing" space is simply reserved during formatting for file system information... it's why you can have a file with a really long name that's still shown as taking up zero space on the drive. Those file names and other metadata have to be stored somewhere.

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  • Reserving 10% of the capacity for file system information seems a lot to me.
    – Bernhard
    Aug 4, 2012 at 13:35
  • @Bernhard You are correct. Only about 50 MB is in file system overhead. Use of NTFS would cut down on this but at the cost of compatibility with non-Microsoft equipment. Feb 9, 2017 at 5:26

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