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PC (Intel x86) desktop CD - For almost all PCs. This includes most machines with Intel/AMD/etc type processors and almost all computers that run Microsoft Windows, as well as newer Apple Macintosh systems based on Intel processors. Choose this if you are at all unsure.
Warning: This image is oversized (which is a bug) and will
not fit onto a standard 700MiB CD. However, you may still test it using a DVD, a USB drive, or a virtual machine.
64-bit PC (AMD64) desktop CD - Choose this to take full advantage of computers based on the AMD64 or EM64T architecture (e.g., Athlon64, Opteron, EM64T Xeon, Core 2). 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.
64-bit Mac (AMD64) desktop 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.
Mac (PowerPC) and IBM-PPC (POWER5) desktop CD - For Apple Macintosh G3, G4, and G5 computers, including iBooks and PowerBooks as well as IBM OpenPower machines.
Warning: This image is oversized (which is a bug) and will
not fit onto a standard 700MiB CD. However, you may still test it using a DVD, a USB drive, or a virtual machine.
Fonte:
http://cdimage.ubuntu.com/daily-live/current/