Q: I recently purchased a 30GB iPod with Video. When I connected the iPod to my PC and checked iTunes, the available disk space is displayed as 27 GB. Is this normal or should I log a complaint with Apple?
A: Believe it or not, this is completely normal, and in fact is standard procedure for any hard drive based device.
The problem stems from the fact that computer storage measurement units are calculated differently between software and hardware. In software, a kilobyte (KB) is measured as 1,024 bytes, a megabyte (MB) as 1,024 KB, and a gigabyte (GB) as 1,024 MB. Therefore, from a software and operating system point of view, 1 GB is actually 1,073,741,824 bytes.
Unfortunately, a number of years ago, hard drive manufacturers started using a different basis for measuring storage capacity, presumably for marketing reasons. The result is that to a hardware manufacturer, a kilobyte is 1,000 bytes, rather than 1,024, and so forth. Therefore, 1 GB to a hardware manufacturer is an even 1,000,000,000 bytes.
So, when you buy a hard drive that is labeled as 30 GB, it is actually 30,000,000,000 bytes, give or take a few. However, to the software on your computer, 30 GB should be 32,212,254,720 bytes. Therefore, as far as your operating system is concerned, the “30GB” hard drive falls somewhat short of this number. If you actually do the math, the “30GB” hard drive actually works out to 27.94 GB of actual capacity. A little bit more of this is lost to some of the operating system format and internal iPod files that are placed on the hard drive, but for the most part, this difference is based on simply the difference in measurement between what the hardware vendors are selling, and how software calculates storage capacity.
Note that this problem is not in any way unique to the iPod, but rather applies to all hard drives in any computer system. If you check the hard drive in your computer, you will discover that the same discrepancy applies. For example, a MacBook Pro with a 100GB hard drive actually only shows 93.1 GB of space as far as the operating system is concerned.