Ubuntu is distributed on three types of images described below.
Desktop CD
The desktop CD allows you to try Ubuntu without changing your
computer at all, and at your option to install it permanently later.
This type of CD is what most people will want to use.
You will need at least 256MB of RAM to install from this CD.
Choose this to take full advantage of computers based on the AMD64 or EM64T
architecture (e.g., Athlon64, Opteron, EM64T Xeon). If you have a non-64-bit
processor made by AMD, or if you need full support for 32-bit code, use the
Intel x86 images instead. This image is adjusted to work properly on Mac
systems.