The Dreamcast had three major hardware variations, usually referred to as v0, v1, or v2 consoles. U.S. and PAL consoles can be identified easily through the sticker on the bottom of the console, which will have the version number in a circle printed on it.
v0 consoles are known for their heatpipe cooling system, which can be identified by the metal fan shroud from the outside of the console. v1 consoles use 5V levels on the G1 bus, creating a compatibility issue with G1 devices designed for 3.3V levels. v0 units are more common in Japan. These models have a separate GD-ROM daughterboard.
v1 consoles are the most common in the United States and Europe, and are the most compatible with Dreamcast mods. These consoles have plastic fan shrouds, a 3.3V level G1 bus, and a separate GD-ROM daughterboard.
v2 consoles are less common, and have the GD-ROM functionality built directly into the motherboard, so the GD-ROM cannot be replaced with an optical drive emulator device. They have plastic fan shrouds and 3.3V level G1 bus. Some later v2 consoles came fitted with firmware v1.022, which disables MIL-CD booting, so CD-based software like homebrew and indie games cannot be used without a BIOS modification.
An unofficial variation of the console is the portable Chinese Treamcast.