The MC68020 (with the MC68851 memory management unit), MC68030, MC68040, MC68LC040 and MC68060 are the only CPUs in the 68000 family supported by Linux/m68k, because Linux (like other Unix-like operating systems) requires a memory management unit (MMU) for protected and virtual memory support. The “m68k” stands for the Motorola 68000 series of processors, found at the heart of popular computers like the Apple Macintosh, the Amiga, the Atari ST and its successors (the Atari TT, Medusa and Falcon), as well as the Sun 3, NeXT, Hewlett-Packard/Apollo Domain workstations and others. In all the attention given to ports to ever more exotic hardware, it's easy to overlook the first production quality port: Linux/m68k. In the five years since Linus wrote those words, Linux has been ported from its Intel roots to a number of other architectures: the ports to the Alpha and Sparc processors are probably the most familiar to readers of Linux Journal.
“Linux is NOT portable (uses 386 task switching etc.), and it probably never will support anything other than AT-hard disks, as that's all I have.” -Linus Torvalds, August 25, 1991.