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Hard Drive free space?

Discussion in 'Computer Components' started by uczmeg, Dec 9, 2004.

  1. uczmeg

    uczmeg
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    Hi,

    Just plugged a 250gb external HD into my PC (XP pro, sp2) and the disk management tool is only reporting 233gb free.

    Is this normal? 17gb seems a lot to vanish?!

    Cheers
    Marc
     
  2. HarshKarma

    HarshKarma
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    This is probably due to the difference in the way manufacturers and computers calculate size.

    Manufacturers use metric; 1GB = 1000MB.
    Computers us binary; 1GB = 1024MB.

    Of course, if you do the calculations, there's still a difference (on mine as well). I assume this is down to the OS, perhaps trying to be more accurate? (A 1 bit file will take something like 4K on the disk).
     
  3. uczmeg

    uczmeg
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    Thanks for that.

    Not realising this had been replied too (no email) I asked the suppliers and they said the same thing...

    Hard drive manufacturers market drives in terms of decimal (base 10) capacity.

    In decimal notation, one megabyte (MB) is equal to 1,000,000 bytes, and one Gigabyte (GB) is equal to 1,000,000,000 bytes.

    Programs such as FDISK, system BIOS, and Windows use the binary (base 2) numbering system. In the binary numbering system, one megabyte is equal to 1,048,576 bytes, and one gigabyte is equal to 1,073,741,824 bytes.

    Capacity Calculation Formula
    ----------------------------------

    Decimal capacity / 1,048,576 = Binary MB capacity

    Example:
    --------

    A 40 GB hard drive is approximately 40,000,000,000 bytes (40 x 1,000,000,000).

    40,000,000,000 / 1,048,576 = 38,162 megabytes

    In the table below are examples of approximate numbers that the drive may report.

    Decimal Binary MB Windows Output
    20 GB 19,073 MB 18.6 GB
    40 GB 38,610 MB 37.3 GB
    60 GB 57,220 MB 55.8 GB
    80 GB 76,293 MB 74.5 GB
    120 GB 114,440 MB 111.7 GB
    160 GB 152,587 MB 149.0 GB
     
  4. Seth Gecko

    Seth Gecko
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    Bear in mind that, using NTFS on XP, you have 3 copies of the MFT so that takes some away.

    It's annoying when you know you have 320GB in a raid yet can only see 305......
     

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