This is because the hard drive manufacturers say a gigabyte is 1000 megabytes, and 1 megabyte is 1000 kilobytes, rather than 1024 like windows reads it.
Hi CNET,
I recently purchased an ASUS T100 2-in-1 Tablet/Laptop.
It was advertised to have 64 GB of SSD memory; however, when I look at it only 58.2 GB is free and 58 GB when formatted.
My question is where did the 6 GB go? When I look at my C drive only 36.1 of 49.3 GB are free. Where does the difference between 58 GB and 49.3 GB go?

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