Where's my 7.7 Gigs? Missing space on my Macbook.

November 23, 2007 10:53 PM

I have a 100 GB drive in my Macbook. Formatted, it appears as as 92.7 GB according to the Leopard Disk Utility. I've used 37.7 GB, and both the Disk Utility and Finder state that I have 47.3 GB free. So where's the missing 7.7 GB?

92.7 - 37.7 = 55 GB, not 47.3 GB.

I've booted from the Leopard DVD and I've run the Disk Utility's repair on both the volume and drive. No problems were found.

Here's a screenshot of disk utility including the used and free space:

http://menino.com/temp/missing.jpg

Anyone know how I can get this 7.7 GB back?

posted by MiG to Computers & Internet (11 answers total)

http://en.wikipedia.org/wiki/Gigabyte
They aren't there. The gigs they're advertising are 1000^3 bytes, the gigs your system is measuring are 1024^3 bytes. It's an advertising trick.
posted by agentofselection at 11:02 PM on November 23, 2007

Response by poster: I don't think that's what's going on.

It's advertised as 100GB (1000^3), but Mac OS X says 92.7GB (1024^3).

I'm ok with 100GB = 92.7GB. I understand that bit.

But 92.7 - 37.7 should still be 55, right? This is Mac OS X making the calculation, not marketing people. But it still says 92.7 - 37.7 = 47.3. Take a look at the screenshot to see what I'm talking about.

So I guess I'm not really complaining about the advertised capacity of the drive, but how Mac OS X determines how much free space I have.
posted by MiG at 11:06 PM on November 23, 2007 [1 favorite]

Wow, I apologize for not reading the question correctly. I have nothing helpful to add here after all.
posted by agentofselection at 11:13 PM on November 23, 2007

Best answer: agentofselection, that was already accounted for in the 92.7GB original disk space.

MiG, people seem to reporting hidden files and directories as a result of failed backups or iDisk syncing. Take a look in this thread.
posted by junesix at 11:16 PM on November 23, 2007

Response by poster: I'm thinking that even hidden files would be accounted for in the "used disk space" of 37.7GB, right?

Here's what du -cxhd 1 / reports:

 24K	./.fseventsd
240M	./.Spotlight-V100
  0B	./.Trashes
  0B	./.vol
5.3G	./Applications
7.5M	./bin
  0B	./cores
512B	./dev
1.0K	./home
3.0G	./Library
1.0K	./net
  0B	./Network
1.1G	./private
5.3M	./sbin
3.2G	./System
 21G	./Users
943M	./usr
4.0K	./Volumes
 35G	.
 35G	total

(I emptied the trash and gained 2GB).

df -g gives this:

Filesystem    1G-blocks Used Available Capacity  Mounted on
/dev/disk0s2         85   35        49    42%    /
devfs                 0    0         0   100%    /dev
fdesc                 0    0         0   100%    /dev
map -hosts            0    0         0   100%    /net
map auto_home         0    0         0   100%    /home

Weirdly, the df command says I only have 85GB in total, not 92.7GB. A difference of 7.7GB! Weird. I'm going to go read some of those threads linked by junesix.
posted by MiG at 11:29 PM on November 23, 2007

Best answer: Ok, problem solved. Here's what I did:

booted from the Leopard DVD, ran the terminal. From the terminal, I used the diskutil command to make sure the volume used the entire partition.

It was using about 100megs below the limit shown in the 'diskutil resizeVolume disk1s2 limits' command. So I set the volume to use all available space. Rebooted, and viola, I have my full 92.7GB available.

Thanks for the pointer to the forums, junesix -- that's how I learned about the diskutil resizevolume command.
posted by MiG at 11:58 PM on November 23, 2007

You did look for bad blocks in those unused 100 megs before you slapped them back into your partition, didn't you?
posted by ikkyu2 at 1:59 AM on November 24, 2007

However, there are a lot of computers out there that do not have the maximum space they say they do - I worked in a shop that sold these computers and I regularly noticed that the disk space was not quite as extensive as it says it was. It seems like they round up the figures to make it look more impressive. Yet, I could be wrong.
posted by bobbyone at 4:31 AM on November 24, 2007

I don't know how much RAM you have, but here are three killer items...

If you have an idisk you may have it set for a local image (takes up 10 gig (I think it's mentioned above))

The Swap space for virtual memory.
The sleepimage space (physically matches your ram, as you put your system to sleep)

My favorite tool for this is Grand Perspective
posted by filmgeek at 4:44 AM on November 24, 2007

The reason for the difference bobby mentioned is the deceptive marketing practices of hard drive manufacturers. In the computer industry, 1 GB is considered to be 2^30 (2 to the 30th power) bytes, which comes out to about 1.074 billion bytes. In the hard drive market, they consider 1GB to be exactly 1 billion bytes. Essentially, they made up their own definition of (kilo/mega/giga/tera)byte that is in multiples of 10, without regard for the fact that these terms were already well known to express quantities in multiples of 2.

Once you install a 1 billion byte drive into your computer, the computer will (correctly) identify it as only 0.93GB, or 7% less than you thought you were getting. Seagate and Western Digital have both settled lawsuits over this deceptive practice, but there are no signs of it ending any time soon.

Also, the disparity grows worse every time we jump up a notch in the units. 1TB drives are getting more and more common now, and a 1TB drive will have 1 trillion bytes, or 9% less than a real terabyte (1.10 trillion bytes).
posted by knave at 7:06 AM on November 24, 2007

In all fairness to Seagate and Western Digital, you could argue that the operating system should identify 1 billion bytes as one 'GB' to follow along with the SI prefixes like every other measurement in existence (including processor speed which isn't measured with powers of two). I mean, it's not the hard drive manufacturer's fault the OS reports the wrong amount. /devil's advocate

This isn't to say that what they did was right. There is a long established history of using powers of two instead of powers of ten with computer hardware measurements and changing it now is about as likely as the United States switching to metric. Most people think the Gibi, Mibi, etc prefixes sound stupid and hardly anyone uses those in serious discussions. I just wish computer measurements had used the metric prefixes in the first place so this entire problem could have been avoided. But it probably seemed like a good idea at the time.
posted by Green With You at 7:55 PM on November 24, 2007