[axelheyst]

Hello,
I have a fresh install of OSX 10.6.3 on a new MacbookPro 15". The HD is 500 GB. When I look in Disk Utility I see this:

Capacity: 499 GB
Available: 488 GB

however, when I look at a disk usage analyzer (like GrandPerspective) it shows:

Volume Size: 465 GB
Free: 455 GB

In addition, when I pull up Boot Camp Assistant, it's also showing:

Volume: 465 GB
Free: 455 GB

So ... where did the 35 GB of space go? It seems like both the Boot Camp Assistant and the GrandPerspective (disk usage analyzer) are only seeing my primary volume (internal HD) at 465 GB of capacity.

Thanks, in advance!

Images:

[reader50]

You're seeing the drive size reported in straight decimal size (499/500) as the HD manufacturers do. Starting with Snow Leopard, Apple gave in and started using their sizing methods too. Where 1 KB = 1,000 bytes.

The other utilities use traditional binary based computer memory sizes, where 1 KB = 1,024 bytes = 2^10 bytes. For a more detailed discussion, see this post. Skip down to Question 2 in the post.

[axelheyst]

Originally Posted by reader50 

You're seeing the drive size reported in straight decimal size (499/500) as the HD manufacturers do. Starting with Snow Leopard, Apple gave in and started using their sizing methods too. Where 1 KB = 1,000 bytes.

The other utilities use traditional binary based computer memory sizes, where 1 KB = 1,024 bytes = 2^10 bytes. For a more detailed discussion, see this post. Skip down to Question 2 in the post.

Thank you very much!

[bishopazrael]

Reader thanks for posting that that's awesome.

[ghporter]

This question comes up now and then, and I think it should be part of every computer enthusiast's education, whether they're interested in the nuts and bolts or not. "Kilobytes" refers to two different quantities, depending on who uses the term. It is flatly unacceptable that different entities use the same technical term to reflect different things, but it's a fact of life. Please note that, while it's supposed to be an advertising gimmick to keep manufacturers out of trouble, the fine print in computer and hard drive ads almost always gives you a heads up: "X bytes refers to Y,000,000 bytes of storage on an unformatted drive" or some such text.

If you look at two different utility apps' indications of hard drive space or usage, and those numbers are "kinda close" as in the comparison above of DU and GrandPerspective, just expect that one reflects a decimal value and the other (smaller value) reflects a binary value. Also, many utilities report both the shorthand ("499 GB") and the longhand ("499,548,344 kilobytes"*), so if you have the longhand, compare that.

Finally, there was once a movement to standardize this sort of nonsense by INSISTING that computer and drive makers used "K" for decimal storage listings and 'k' for binary listings. Yes, case is important here (we frequently use case to differentiate between Bytes and bits...), and many manufacturers actually do use this notation. Just not everybody.

*those are numbers I pulled out of my ear; they are probably wildly off from what "499GB" would really equate to. It's too early on Saturday for me to bother with math.

[jmiddel]

Well, 499,000/1024 =487,3046, which leaves 22G unaccounted for. Thanks to reader50's suggestion I found a ton of extra space on my HD, logging in as root and running Omnidiskweeper, a free utility that lists all your files in order of magnitude. OmniDiskSweeper - Products - The Omni Group

[CharlesS]

499,000,000,000 bytes / (1024^3 GiB/bytes) == 464.73 GiB, which rounds up to 465 GiB.

Unfortunately, the binary prefixes (KiB, MiB, GiB, etc.) are the only way to be absolutely clear about which units you're actually talking about, so that's what I'm electing to use these days.

[ghporter]

So "KiB" = 1024 bytes, "MiB" = 1024^2 bytes, "GiB" = 1024^3, and so on... I believe this notation works better than the "KB" vs "kB" notation that was going around a few years ago - and never got any traction.