While Dreamcast games are similar to CD-ROM, the actual optical disc used is proprietary, and can hold up to 1.2 gigabytes of information. This is a lot of space -- most games use only a fraction of it for the actual game. What can eat up the space are the incredible full motion video intros and intermissions included in most Dreamcast games.
The Dreamcast has a drive similar to other CD-ROM drives, but the optical disc is proprietary.
There is a noticeable delay while the game is loaded from the CD, which you do not get with cartridge-based games. Of course, the trade-off for faster loading is a significantly smaller amount of storage on a cartridge. Most Dreamcast games use a customized version of Microsoft Windows CE as their operating system; but some use Sega's proprietary Dreamcast operating system.
Dreamcast CDs are just as susceptible to scratches and intense heat as normal CDs. Even more so in fact, since a scratch on a game CD can make it totally unusable.
The games available for the Dreamcast cover all the categories, and its library of games is increasing rapidly. Game prices range from under $20 for certain preplayed titles to over $75 for some of the hottest new games.