500 GB hard disk lost 40GB during reformatting

Discussion in 'Mac Basics and Help' started by nehas91, Jan 23, 2011.

  1. nehas91 macrumors member

    Oct 26, 2008
    Yesterday, I was trying to install Windows 7 on my 2009 Unibody Macbook Pro using Bootcamp. I selected 40 GB for the windows partition but it was unable to partition it and gave me an error saying something about how bootcamp was unable to move some files. So I opened disk utility and verified and repaired disk permissions - it told me to boot from the OSx CD and fix it that way. So I thought why not reformat the computer while I have the installation disk out. So I pop in the installation disk, boot from it, open disk utility to erase the hard drive and it shows me that I only have 465 GB on the HDD and beside that number in parenthesis is 500GB. Now I'm wondering where did the other 40BG go? I've reformatted the hard drive twice since yesterday and the HDD still displays that the hard drive has 465GB. Shouldn't it be something like 499GB? Anybody have any ideas as to what's going on? How can I fix it, and get the remaining 40gb. I remember when I first got my laptop and installed Snow Leopard, it showed me that the harddrive had 499GB on it and went down to something like 489 after 11gb of installation. How come it's showing me 465gb now? Shouldn't it go back to 499gb since I've erased the hard drive and reformatted?
  2. smirk macrumors 6502a


    Jul 18, 2002
    Orange County, CA
    Are you sure you remember it showing you 499 GB free when you first got it? Losing 40 GB sounds normal to me. Hard drive manufacturers measure the 500 GB at 1,000 bytes per kilobyte, while computers measure it at 1,024 bytes per kilobyte.

  3. Joewebster macrumors member

    Jan 20, 2010
    New York
    I'm with smirk, I remember being pissed when I formatted my drive in my first computer, and it was like 30 gigs less than advertised. It sucks, but thats the way it works :/

    and by the way, here's a handy guide:
  4. Makosuke macrumors 603

    Aug 15, 2001
    The Cool Part of CA, USA
    Just for reference, you can find out how many GiB (Gibibytes, a recently-defined term for binary gigabytes being 1024*1024*1024 bytes) by taking the drive's stated size in GB (meaning decimal Gigabytes, 1000*1000*1000 bytes) and dividing by 1.074. That's the factor that 1024^3 gets you.

    So for example, if Seagate sells you a 500GB drive, and you want to know how many GiB it is (which is to say the number of GB Windows or the MacOS prior to 10.6 will tell you), 500/1.074 = 465.5GB. Which is of course exactly what you've got. This has been true for every OS for a long while, it's just gotten more noticeable with GB and TB drives (TBs are a whole 10% off).

    HOWEVER... Snow Leopard actually reports drive sizes in binary GB. So if you install 10.6, it will report your 500GB drive as 500GB. It's not any bigger--every file size on the drive will be displayed as if it were a little larger than previously, or with Windows--but it'll be the number you expect. So if you want to feel better/less confused about your drive, you can go spend $30 on Snow Leopard.

    Come to think of it, I wonder which size iOS uses. Presumably binary GB as well, although you access the filesystem directly so rarely it doesn't really matter.

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