There are now so many ARM processors in the world that it seems now to have completely overshadowed all other processor types/families/designs.
Now, I'm not one for monopolies in any market; but for years we had precisely that with the old and creaky Intel x86 type (a close clone of which was and is also made by AMD, and once upon a time a third company did the same of code-compatible chips as well).
I always think of them, and the computers with them inside, as 'HGV machines', as per my years-old saying about being like "taking a lorry out to do the shopping", because of the power, memory and other resources they take just to get going, and the heat and noise they pump out as a consequence..
These days the processor chips have silly names such as Athlon and Celeron (Pentium was a much better name!) but essentially they are somewhat distant (by now) cousins of the ancient 386 and 486 processors.
ARM has its own in-brand names such as Cortex, but at least they sound technical...
Anyway, the two important distinctions to make are (a) that the ARM is a much more elegant design, and (b) that it is made under licence by many companies, not just one or two. Indeed, some of those companies, working with the ARM people, have designed their own ARM-based designs, from Digital's StrongARM of 1996 to a Chinese design for a complete System-on-Chip (SoC) on which work started a year or so ago.
There are now billions of ARM chips on the planet; and with the approach of ARM Holdings' quarter 2 results for 2012, due out in a couple of weeks from now, it is instructive to look back at last year's results for the same quarter. There are several interesting facts and figures in the "points of interest" section on the linked page, but the first one tells the main story: 1·1 billion ARMs shipped during those three months last year.
The second point there reflects something I have mentioned before, which is that forthcoming market-leading Operating Systems will be coded to run on ARM systems. This is what I believe is termed "waking up and smelling the coffee" on the part of the likes of Microsoft and Google. The world has moved on, in a positive direction, and they can't afford to ignore or sideline it any longer.