All Power Macintosh before the G5 are 32-bit PowerPC; the G5 is the first 64-bit Macintosh. Information about very old (pre-PCI) Macs can be found at the NuBus Linux project; all others are PCI-based and contain other common hardware like AGP. USB, ATAPI (IDE), and IEEE1394 (Firewire). Aside from PCI/NuBus, the other major hardware division is “New World“, meaning iMac and later, and “Old World“, meaning pre-iMac.
A variety of well-known Linux distributions run on Macs. See the complete list for your favorites.
New World Macs use the yaboot bootloader.
Altivec is a feature of G4 and G5 CPUs that can process certain types of data very quickly. Some Linux programs, such as DVD players like mplayer, ogle, and xine, can use Altivec to accelerate data streaming.
Developers wishing to exploit Altivec should consult the Development Page.
Like Sun servers and IBM pSeries, Macs use Open Firmware, also known as IEEE1275. Old World Macs tend to have very buggy firmware implementations, while New World Macs are much better (which facilitates booting Linux directly from firmware). A good amount of OF documentation can be found in the NetBSD macppc FAQ.
New World Open Firmware can boot from the network, which is very convenient for development and testing new kernels.
Macintosh do not use the DOS partition map scheme typical of PCs, so well-known tools such as fdisk, sfdisk, and cfdisk will render your disk unbootable. (The real issue is that your firmware must understand your partition layout, and Apple’s firmware only understands Apples partition map.)
Instead, Apple defined its own partition format, and to manipulate an Apple partition map, you need a tool that understands it. Currently only pdisk and GNU parted do. (pdisk is called mac-fdisk by Debian and Gentoo, because they like to be different.) pdisk is unmaintained, and GNU parted is much more user-friendly.