Did you Know . . . Why Your iPod's Capacity Appears to be Less than Advertised Forty gigabytes is a huge amount of music—around ten thousand four-minute songs. Even four gigabytes can hold a thousand songs, enough to keep you quiet (if that’s the word) for nearly three days of solid listening. But unfortunately, you don’t actually get the amount of hard disk space that’s written on the iPod. There are two reasons for this. The first (and eminently forgivable) reason is that you lose some hard-disk space to the iPod’s OS and the file allocation table that records which file is stored where on the disk. This happens on all hard disks that contain operating systems, and costs you only a few megabytes. The second (and much less forgivable) reason is that the hard-drive capacities on iPods are measured in “marketing gigabytes” rather than in real gigabytes. A real gigabyte is 1024 megabytes; a megabyte is 1024 kilobytes; and a kilobyte is 1024 bytes. That makes 1,073,741,824 bytes (1024 × 1024 × 1024 bytes) in a real gigabyte. By contrast, a marketing gigabyte has a flat billion bytes (1000 × 1000 × 1000 bytes)—a difference of 7.4 percent. So your iPod will actually hold 7.4 percent less data than its listed drive size suggests (and minus a bit more for the OS and file allocation table). You can see why marketing folks choose to use marketing megabytes and gigabytes rather than real megabytes and gigabytes—the numbers are more impressive. But customers tend to be disappointed (to say the least) when they discover that the real capacity of a device is substantially less than the device’s packaging and literature promised. Almost all hard-drive manufacturers give capacities in marketing gigabytes, which has conferred herd immunity on them so far. At this writing, a class-action lawsuit about this double-system of measurements is in the works, and might force manufacturers to state the capacity less ambiguously. A previous class-action lawsuit forced monitor manufacturers to state the viewable screen size of cathode-ray tube monitors as well as the size of the screen itself (part of which is cut off by the monitor bezel). This is why you see monitor ads that state “15" monitor, 13.7" visible”; before the lawsuit, the ads simply claimed “15" monitor.” | 
