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Why is the effective hard drive size lower than the actual size?

I just purchased a Dell Inspiron 1410 without OS. In the BIOS, it shows 320 GB of hard disk space. After I installed Windows 7 Ultimate, only 299 GB total hard disk space is shown. I only got one partition. I run a partition manager, it shows only 299 GB, without any partition that has the other 20 GB.

Can somebody try to explain what had happen? What will I do so I can use all of the 320 GB.

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The BIOS (or the HD manufacturer) is measuring with 1 GB = 109 bytes = 1.000.000.000 bytes.

The Windows file dialog seems to count in GibiBytes, where 1 GiB = 230 bytes = 1.073.741.824 bytes

Checking the numbers, 299 * 230 is approximately 320 * 109.

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Basically a 320GB disk isn't 320GB, it's to do with the mixed use of 1000 and 1024 (210) between marketing and operating system, never expect the full amount OK.

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  • 6
    actually, a 320GB disk is 320GB, just read the units(7) man page
    – alexanderpas
    Jun 16, 2010 at 19:02
  • 4
    It's not a mix-up between marketing and operating system, it's a mix-up between the metric system and lazy programmers.
    – endolith
    Sep 4, 2010 at 20:10