I've looked into this a bit.
As noted previously, it is essentially impossible to figure out exact shipments of 8051,
as there is no central clearinghouse of licensees, and there are literally dozens of
suppliers sticking 8051 IP in all sorts of things. That said, according to the only
reasonably well cited analyst report I have (from Emitt Solutions), the 8051 architecture
accounted for 19% of the US$4.9 billion 8-bit MPU market in 2007. If you wave your hand
and say the average volume price across all 8051 variants is US$0.25 (a number I think is
probably high), that's around 40 billion units shipped in 2007.
According the Annual Report for ARM Holdings, Plc., there were shipped 2.6 billion ARM
processors for mobile applications and 1.4 billion in other applications from all licenses
in 2008. This was up from around 3 billion units in 2007 (in a total market for 32-bit
embedded processors of around US$3.8B). Safe to assume it was more than that in 2009. Not
sure what that represents as a revenue number, as ARM Holdings revenue numbers are for
licensing fees. However, one could guess it's a market of significantly more than
US$4b across all licensees in 2008.
By comparison, Freescale did around US$1.88B in microcontroller sales, but that was across
all their lines (including the still very popular 68xx/HC lines), so is safe to assume the
actual units shipped for PPC is a fraction of ARM numbers. I know there are other PPC
licensees, but I don't think they're going to make up that gap.
All analysts agree that the 8-bit market is eroding and the 32-bit world is exploding,
from a market share if not revenue perspective.
KJ