There has been a fair bit written about Sweet 16 - a 16-bit virtual processor devised by Steve Wozniak in 1976/77 in order to simplify the handling of 16-bit instructions on the Apple 1 - which was an 8-bit 6502 and was somewhat short of registers.

Woz devised a virtual 16 bit machine with a bank of 16, 16-bit registers located in the first 32 bytes of zero-page RAM.

Modern languages (specifically C) need a bank of general purpose registers and so the implementation of a 16-bit virtual machine on top of the raw cpu, was one way to simplify programming.

The details of Sweet16 can be found here http://www.6502.org/source/interpreters/sweet16.htm

16 is a good number of registers! (OPC, MSP430, ARM,...) Although of course 8 is also a choice with some history.

Charlie Hitselberger loves golfing around with his Pettil, and came up with a couple of cool observations and insights about Sweet16 here:

Mike B.

(Thanks! Here's an archived version in case tumblr evaporates.)