Why does my 1TB hard drive suddenly only show 931 GB of space?

Larry Campbell March 26, 2013
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My FreeAgent Goflex portable hard drive was 1 Terabyte, but now reads 931 GB. I know I can’t get it all back to 1 TB, but 69 GB is a lot of space lost. Is there something to claim any of this back?

  1. Alan Wade
    March 27, 2013 at 5:01 pm
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    March 27, 2013 at 6:47 am

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  3. Ajinkya Datalkar
    March 26, 2013 at 7:51 pm

    if you are using windows then, goto start =>search =>type administrative tools =>computer management => storage =>disk management. check if there is any unallocated space. i had a 40GB external hard disk which was showing 37.2GB when i had connected it to my computer, later i had connected to my friends computer having linux installed,it was showing 35GB .....when i connected it back to my computer it was still showing 35GB...in disk management it showed two partitions on the disk..one was accessible and the other was not accessible...i formatted it and later it was showing 37.2GB...try using mini partition tool....bcoz i have a 1TB HDD installed on my cmputer but it has created a system reserve space of only 99.8MB...i don't think in any case your computer will create a system reserve space of 69GB....

    U MIGHT HAVE DONE THIS I HAVE JUST TRIED TO ANSWER....
    SORRY FOR BAD ENGLISH :-(

  4. Jules Dadi
    March 26, 2013 at 3:40 pm

    Well from my own experience, anytime you plug in another storage device some space 'disappears'. i believe its because your system synchronizes with the device and then reserves space for system stuff.

  5. Bruce Epper
    March 26, 2013 at 3:31 pm

    This space is not "lost". Drive manufacturers report drive sizes using base 10 math while computer operating systems tend to report these sizes using base 2 math. The advantage of using base 2 math means that the code is somewhat simpler and it will run faster. The DIV instruction to carry out the base 10 math will end up executing at least 4 times longer than doing SHR instructions for the base 2 math (minimum of 41 cycles as opposed to a maximum of 10). If there are cache misses, NAN errors, etc., the number of clock cycles for the DIV instruction can result in 100 cycles or more being added to the time required to perform the operation. This does not take into account the possibility that more registers may need to be preserved (stored elsewhere) for the DIV instruction than the SHR instruction and recovered afterwards increasing the execution time even more. Because of all of this, instead of dividing by factors of 1000 (or shifting 3 decimal positions) we are shifting 10 binary positions effectively dividing by factors of 1024. The end result is that a hard drive labeled by the manufacturer as being 1TB will be reported by most operating systems as 931GiB.

  6. Alan Wade
    March 26, 2013 at 2:20 pm

    There is no industry standard for hard drives.
    All companies advertise their hard drives as 1TB for example based on a 1000 bytes to a KB and so forth when the true figure is 1024 which is what your computer reads.

    There was another discussion on this a while back where I did all the maths for one guy but I cant find it just now.

  7. ha14
    March 26, 2013 at 12:06 pm

    a kilobyte means 1024 bytes
    1,000,000,000,000 bytes = 976,600,000 kilobytes = 953,674 megabytes = 931.3 gigabytes = 0.905 terrabytes. so true 1TB = 1000 GB would be 1,099,511,627,776 bytes

    also there are some space reserved for the system of the hard drive.

    • Piseth Mao
      March 26, 2013 at 4:09 pm

      If I were the owner of this question, I would mark this answer as the solution to it. It is very easy to understand and gets to the point. I've never thought about the calculation problem before, only space reserved for the system.

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