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Thread: Drive Capacity explained

  1. #1
    My Name is.... TZ Veteran Stripe's Avatar
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    Drive Capacity explained

    I found this article regarding drive size capacity and why the advertised size is always bigger than the formatted size....

    Question
    Why is my drive displaying a slightly less than expected capacity in Windows or Mac?

    Answer
    Determining drive capacity can be confusing at times because of the different measurement standards that are often used. When dealing with Windows and Mac based systems, you will commonly see both decimal measurements and binary measurements of a drive's capacity. In either case, a drive's capacity is measured by using the total number of bytes available on the drive. As long as the drive displays the correct number of bytes (approximate), you are getting the drive's full capacity.

    Decimal vs. Binary:
    For simplicity and consistency, hard drive manufacturers define a megabyte as 1,000,000 bytes and a gigabyte as 1,000,000,000 bytes. This is a decimal (base 10) measurement and is the industry standard. However, certain system BIOSs, FDISK and Windows define a megabyte as 1,048,576 bytes and a gigabyte as 1,073,741,824 bytes. Mac systems also use these values. These are binary (base 2) measurements.

    To Determine Decimal Capacity:
    A decimal capacity is determined by dividing the total number of bytes, by the number of bytes per gigabyte (1,000,000,000 using base 10).

    To Determine Binary Capacity:
    A binary capacity is determined by dividing the total number of bytes, by the number of bytes per gigabyte (1,073,741,824 using base 2).

    This is why different utilities will report different capacities for the same drive. The number of bytes is the same, but a different number of bytes is used to make a megabyte and a gigabyte. This is similar to the difference between 0 degrees Celsius and 32 degrees Fahrenheit. It is the same temperature, but will be reported differently depending on the scale you are using.

    --------------------------------------------------------------------------------

    Various Drive Sizes and their Binary and Decimal Capacities

    Drive Size--------Approximate--------Decimal Capacity--------Approx Binary Capacity
    in GB--------------Total Bytes------(bytes/1,000,000,000)-----(bytes/1,073,724,841)
    10 GB-------------10,000,000,000------------10 GB------------------------9.31 GB
    20 GB-------------20,000,000,000------------20 GB------------------------18.63 GB
    30 GB-------------30,000,000,000------------30 GB------------------------27.94 GB
    40 GB-------------40,000,000,000------------40 GB------------------------37.25 GB
    60 GB-------------60,000,000,000------------60 GB------------------------55.88 GB
    80 GB-------------80,000,000,000------------80 GB------------------------74.51 GB
    100 GB-----------100,000,000,000-----------100 GB------------------------93.13 GB
    120 GB-----------120,000,000,000-----------120 GB-----------------------111.76 GB
    160 GB-----------160,000,000,000-----------160 GB-----------------------149.01 GB
    180 GB-----------180,000,000,000-----------180 GB-----------------------167.64 GB
    200 GB-----------200,000,000,000-----------200 GB-----------------------186.26 GB
    250 GB-----------250,000,000,000-----------250 GB-----------------------232.83 GB

  2. #2
    Head Honcho Administrator Reverend's Avatar
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    Some Hard Drive manufacturers are currently being sued for advertising incorrect capacities.

    Computer Makers Sued Over Hard Drive Size

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  3. #3
    My Name is.... TZ Veteran Stripe's Avatar
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    heh heh heh....I do think that they're advertising is misleading. But after reading this, I thought is was a good thing to post.

    For example, my OS was reporting a large drive as 128gb's. After using the calculations (128,000,000,000x1,073,724,841), I was able to determine that the drive was being recognized as a 137gb, which is the current threshold of operating systems.

  4. #4
    Security Intelligence TZ Veteran cash_site's Avatar
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    Has anyone had customers ask where did the rest of my HD space go ?? I bought 20GB but only got 18.63GB

    LOL... the manfacturers do make it clear that they measure 1GB=1000 Megabytes.

    Oh well... this will just go round in circles... but as the HD get bigger and the 'lost space' gets bigger, they'll have to make new labels.

    --- 0wN3D by 3gG ---

  5. #5
    My Name is.... TZ Veteran Stripe's Avatar
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    Whats even better is that if you run an install of XP from the CD, you also loose 8MB because the XP install creates a partition to write the data to.

  6. #6
    Silver Member joshsiao's Avatar
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    In the past I had always thought that this "lost space" was due to invalid sectors on the Hard Drive because at that time I was using a very old computer and there would be frequent lost sectors and clusters in the Hard Drive. Thanks Stripe for clearing my doubts. I had actually asked my father once before and he said that its because the manufacturer cannot make it exactly to the advertised amount. I knew that it would never be exact but I could not believe that it could be off by so much. The case is that I just don't like seeing it being lower than the advertised amount of 80GB. Its like there is an unknown 6GB partition which will never be utilitised but now I know its just due ti the usage of different scales. I also think that Stripe's usage of the different temperature scales were good examples. Another example would be 1 inch and 2.5cm, same amount but just different scales.

    Thanks alot Stripe.
    "Never seem more learnt then the people you are with. Wear your learning like a watch and keep it hidden. Do not pull it out to count the hours, but give the time when you are asked."
    ~Chesterfield

  7. #7
    Silver Member joshsiao's Avatar
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    I try not to open threads that won't go very far so I thought maybe I can post my question here:

    When I look at my HD properties, it says that the total disk usage is 3.58GB. But when I look at the properties of all the files stored on the disk, including hidden files, it says the usage is 2.18 GB. I would like to know where the almost 1.5GB of memory went to? I mean its 1.5GB and is it 'lost'?

    I use WinXP Home Edition and the HD has a 74.4GB capacity (Binary scale)
    "Never seem more learnt then the people you are with. Wear your learning like a watch and keep it hidden. Do not pull it out to count the hours, but give the time when you are asked."
    ~Chesterfield

  8. #8
    Hardware guy Super Moderator FastGame's Avatar
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    Hi joshsiao, I think when you look at the HD properties of 3.58gig it includes the space set aside for things such as swap file, system restore, trash bin and master file table. The 2.18 gig is the actual amount of files stored in that space.

    If I'm wrong an expert will soon let us know

  9. #9
    Silver Member joshsiao's Avatar
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    Thanks.
    "Never seem more learnt then the people you are with. Wear your learning like a watch and keep it hidden. Do not pull it out to count the hours, but give the time when you are asked."
    ~Chesterfield

  10. #10
    Silver Member joshsiao's Avatar
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    Oh yeah, regarding the usage of the Hard Drive by Windows, can you give me a list of things that Windows sets asides for because I would like to account for all the memory used. Thanx.
    "Never seem more learnt then the people you are with. Wear your learning like a watch and keep it hidden. Do not pull it out to count the hours, but give the time when you are asked."
    ~Chesterfield

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