How much data can they hold?
There are 21-minute (80mm), 63-minute (120mm), and 74-minute (120mm) CD-Rs. These translate into data storage capacities of 184MB, 553MB, and 650MB, respectively (note these numbers are approximate). You lose a little space because of the leadin and leadout areas, which occupy about 15MB, but you may gain a little space over storage on a hard drive because the “cluster” size is only 2K. CD-Rs may advertise that they hold 650MB, 680MB, or even 700MB of data, even though they all claim to hold 74 minutes of audio. The reality is that they’re all exactly the same size, and you’re not going to get more data onto a 74-minute disc by buying a different brand. Folks interested in “doing the math” should note that only 2048 of each 2352-byte sector is used for data on typical (Mode 1) discs. The rest is used for error correction and other misc fields. This is why you can only put 650MB of data on a disc that will hold 740MB of audio. It should also be noted that hard drive manufacturers don’t
