A machine that takes inspiration from the programming language FORTH¹. It can be seen that the language here is very close to both the stack operations and the traditional machine/assembly language. Hence, programs can use and be optimized in line of being "forthified" (adopted to suit FORTH thinking).

Compile with gcc installed; make at the command line, then run ./fib.

The sample chosen to illustrate extended from the previous vm1-machine is the Fibonacci series: 1, 1, 2, 3, 5, 8, 13 ... which can be defined as a mathematical recursive function:

Applied from the FORTH-thinking we have the following operations at the core:

TWODUP
ADD
ROT
DROP

First duplicate what is already on stack, the two top items TWODUP (or 2DUP), such that if we have "1 2" after would be left with "1 2 1 2". Next add the two numbers on the stack "1 2" becomes "3", and the first two still are there such that "1 2 3". Then rotation ROT would get "2 3 1", and we then DROP the top, "2 3". That is, the numbers that remain will be added next time. And so on.

The experimental enlargement of the machine capacities through new instructions maybe also be compared with the RISC vs. CISC debate² (even if it is on a virtual machine which introduces new aspects that doesn't make it fully comparable). Here RISC (reduced instruction set) indicate microprocessors which have a few (simple, powerful), compared to the CISC (complex instruction set) which have many (complex, "slow") instructions. (A machine with even less instructions, in fact only one, use only the SUBLEQ³ instruction.)

Another observation is that there exist hardware, processors with instruction sets that implements the virtual machine of Java: JVM (at least in its early iterations for embeded use).⁴

Building from the "bottom up" was also something that could be claimed happened to Lisp Machines, that had Lisp Machine Lisp at the hardware level.⁵ Microcode could be used for directly implementing a "high level" language such as PL/I in hardware.⁶ Or indeed in Forth.⁷