Unless you plan to include computer files on your DVD, as we'll discuss in Chapter 20, "Creating DVDs with iDVD," the best way to think of DVD storage capacity with iDVD is in terms of how many minutes of video you can fit on the disc. The amount of video you can fit on a disc is determined by how much the video is compressed. Because iDVD does the encoding automatically, the limit is about 90 minutes of video on the disc.
If you're talking about the disc in terms of bytes and megabytes, however, you might be familiar with the often-quoted measurement of 4.7 gigabytes (GB) ”that is, the claim that you can store up to 4.7 gigabytes of data on a single-layer DVD disc.
This is only partially true. If you were putting data files on a DVD and had 4.7 gigabytes' worth of files on your computer, you'd find that you can fit only about 4.37GB on the DVD ”this has to do with the difference between the way data is stored on a computer hard drive and the way it's stored on a DVD. Essentially, you can store 4.7 billion bytes of data on a DVD, but only about 4.37GB.
But regardless of how you look at it, DVD is an incredible medium. The CD format typically allows only 650MB of data on a disc, whereas the DVD format enables you to put up to 4,370MB on a disc! To put this in perspective, consider that many computers you see on the shelves in stores are likely to have 3.5'' floppy disk drives . Each of these plastic floppies holds about 1MB of data, so a DVD disc holds the equivalent of about 4,370 floppy disks! (See Figure 18.23.)
Figure 18.23. The relative capacities of different storage methods .