The flip side of "no fragmentation" is, there's no ARM core with hardware multithreading, and there won't be one until ARM decides to make one, which AFAIK may

The flip side of "no fragmentation" is, there's no ARM core with hardware multithreading, and there won't be one until ARM decides to make one, which AFAIK may well be "never". You can license a core with hardware multithreading if you need it - say, MIPS from Imagination - but the ISA won't be ARM-compatible. To the extent that ARM's "software ecosystem" is valuable, it's a pity nobody can make a multithreaded ARM-compatible core. Similarly for other features. On the other hand, x86, which is "open" to all of Intel, AMD and VIA who reached a patent war stalemate, has the problem of incompatible instruction set extensions, as documented in "Stop the instruction set war": http://www.agner.org/optimize/blog/read.php?i=25 http://www.agner.org/optimize/blog/read.php?i=25 Which problem is worse is hard to decide.