New MBP, Is This Normal?

Discussion in 'Mac Basics and Help' started by cms2, Sep 10, 2007.

  1. cms2 macrumors 6502


    Aug 4, 2007
    I ordered an MBP with a 160 GB hard drive. When I look at my system profiler under Serial-ATA it says total capacity 149.1 GB. I know that some hard drive is taken up with the OS and whatnot, but that's separate; total available is 141.1. Why is the total capacity only 149? Shouldn't it be more like 160 with 151 available?
  2. aaronw1986 macrumors 68030

    Oct 31, 2006
    No, all hard drives are this way. It's perfectly normal.
  3. varmit macrumors 68000


    Aug 5, 2003
    Removed due to stupidity.
  4. Makosuke macrumors 603

    Aug 15, 2001
    The Cool Part of CA, USA

    This is almost completely wrong, and it's an unfortunate bit of old information that has refused to die.

    The formatting information takes up a very, very small portion of the disk. What you're seeing is a side effect of the fact that all hard drive manufacturers define a Gigabyte as 1,000,000,000 bytes -- base ten. All OSes, however (Mac, Windows, Unix, and Linux at least, probably others as well) use a base-2 system. So 1KB is 1024 bytes, not 1000, 1MB is 1024KB, and 1GB is 1024MB.

    Thing is, when it's only 1KB, that 24 is pretty small. But when you multiply it out, 1GB = 1024*1024*1024 = 1,073,741,824 bytes. Which is 1.073GB in hard drive manufacturer, base 10 GB.

    So if you divide the 160GB (manufacturer) by that 1.073GB (OS), you get 149.1GB (actually a little less--your drive is probably a hair larger than 160GB, which is common).

    Bottom line is, you are getting exactly what you should be--the OS just does the math differently. It's really, really stupid, and should have been fixed one way or the other a long time ago, but that's why on every single HD related advertising thing you'll see a little * pointing out that HD manufacturers calculate a GB as 10^9 bytes. Go have a look at the Tech Specs on the MacBook page at Apple's site.

    RAM, interestingly, is actually done in base-2, OS style, so it's not an issue there.

    There is actually a "corrected" notation now KiB (kibi-bytes), MiB, and GiB for the OS-style base-2 versions, but it's not very popular outside geeky circles so far.

    Here's Western Digital Knowledge base article that may explain it better than I if you're not following:
  5. Neutral Gamer macrumors 6502a

    Neutral Gamer

    Wow, that's a great reply Makosuke. Good explanation. :)
  6. Santa Rosa macrumors 65816

    Santa Rosa

    Aug 22, 2007
    Well in, thats one that needs to be cleared up a lot.
  7. cms2 thread starter macrumors 6502


    Aug 4, 2007
    thanks so much for all the great responses! This site and its great members never fail to impress!
  8. Apple Corps macrumors 68030

    Apr 26, 2003
    Makosuke - that is the type of educational response that is really helpful - Well Done :D

    From the HOT part of California :rolleyes:
  9. 119576 Guest


    Aug 6, 2007
    very well explained, Makosuke.

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