Why do hard drives lose space after formatting?

Severdthumbz May 11, 2011
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Why is it when you by a HDD that states one capacity that after formatting it in either Windows or Linux you lose GBs of space? Is is possible to reclaim that space?

  1. Mike
    May 13, 2011 at 12:25 am

    Manufacturers use decimal SI units (Base 10) for calculation
    Giga = 10^9 = 1.000.000.000

    Computers calculate in Binary (Base 2)
    Giga = 2^30 = 1024^3 = 1.073.741.824

    Even if manufacturers would use Binary calculation and state the Hard Drive space as e.g. 465,66GiB (raw unformatted space) the actual space available for the user is still lower depending on the Partition Format (MBR, GPT, ...) and the used File System (FAT32, NTFS, HFS...).

    When using GPT for example the system will create a 100MB or 200MB hidden partition. This is not much compared to the total space but people still notice it.

  2. Oron Joffe
    May 12, 2011 at 3:31 pm

    Both the contributors above make valid points, but there are really two separate issues.

    First is that hard disc manufacturers quote the capacity of their decimally, wehre kilo=1,000 (and mega=1,000 kilo etc), whereas operating systems usually use the 'binary standard', where kilo=1024 etc. On large modern hard disc this can amount to quite a difference.

    Secondly, formatting discs involves creating a filesystem - a way of organising the files and folders on the disc (a bit like having table of contents, page numbers and indexes in a book), and this uses up some space. Depending on the filesystem, the amount of space can be considerable (in FAT12, of to bad old DOS days, it was 1/3 of the total space!).

    On the other hand, if you enable compression on your drive you will have more space than the stated capacity, so the game can be played both ways!

  3. James Bruce
    May 12, 2011 at 1:20 pm

    ... no

    You didnt lose any space, because it wasnt there in the first place. The states drive capacity is a lie - or rather, a calculation using different methods. 1TB = 940gb, not 1000gb

    Interestingly, OSX uses the same calculation as HD manufacturers, so the 300GB hard disk I plugged in tells me that it is in fact 300gb.

    • Mike
      May 13, 2011 at 12:00 am

      Yes, Apple "adjusted" the calculation [to base 10] with Snow Leopard probably to reduce customer support requests.
      http://support.apple.com/kb/ts2419

  4. Anonymous
    May 12, 2011 at 9:39 am

    in linux Did you set any options when you formatted, or just take the defaults? Try:
    tune2fs -m 0 /dev/foo

    the drive manufacturers are giving you a perception of a larger capacity than it
    really has. A 120 ', is only 114.5Gb to an operating system, It depends on who you agree with, should we change the computing definition of a
    mega/giga to be 1000 instead of 1024 or vice versa?