Originally posted by idea_hamster
As I understand it, the difference between the "descriptive" size of a disk and the actual usable size is not so much due to rounding up as it is the directory and sector information that the computer writes to the disk when it formats it.
I have one of the original 10GB iPods. The formated size of the drive is 9.28GB. You can keep alot of music on a 10GB iPod.
Actually, the discrepancy you see is basically just manipulation on the part of hard drive manufacturers and device sellers to fool you into thinking you get a larger capacity hard drive than you're actually getting.
See, computers usually measure hard drive capacities in GiB, not GB. The GiB is called a gibibyte, and when you see the Finder saying your hard drive has 58.5 GB free, it's actually supposed to be 58.5 GiB.
A gibibyte is 2^30 bytes, or 1024 mebibytes (which is the appropriate term for a what most people think is a megabyte -- 2^20 bytes). A gigabyte is simply 1 billion bytes, where "giga" is the standard SI prefix.
So when you buy a hard drive, the stated capacity is actually in megabytes... since a megabyte is less than a mebibyte, the buyer thinks that the hard drive is larger than it actually is. The computer reports the actual capacity in mebibytes, making it appear that you've "lost" space, when you've really just been the victim of a marketing ploy.
So a 5 GB iPod is actually 4.65 GiB, which is mislabeled as 4.65 GB in the Finder. Similarly, a 10 GB iPod is 9.31 GiB, and a 15 GB iPod is 13.95 GiB, which roughly corresponds to the formatted capacity that you guys are reporting. Yes, information about the drive is stored on the drive and takes up some space, but not nearly as much as the discrepancy that is due to the above problem.
To make it more clear, visit
this site, which should clear it all up if you still have questions. It also offers a bit of history.
In other words, hard drive manufacturers state capacity in GB, MB, and KB, while the computer reports capacity in GiB, MiB, and KiB (but mislabeled as the former units). Because GB, MB, and KB are smaller than GiB, MiB, and KiB, respectively, hard drive manufacturers make you think that you're actually getting more capacity than you think.