Niklaus Wirth specified a simple p-code machine in the 1976 book Algorithms + Data Structures = Programs. The machine had 3 registers - a program counter p, a base register b, and a top-of-stack register t. There were 8 instructions:
P-code machine
In computer programming, a P-code machine (portable code machine[1]) is a virtual machine designed to execute P-code, the assembly language or machine code of a hypothetical central processing unit (CPU). The term P-code machine is applied generically to all such machines (such as the Java virtual machine (JVM) and MATLAB pre-compiled code), as well as specific implementations using those machines. One of the most notable uses of P-Code machines is the P-Machine of the Pascal-P system. The developers of the UCSD Pascal implementation within this system construed the P in P-code to mean pseudo more often than portable; they adopted a unique label for pseudo-code meaning instructions for a pseudo-machine.
stack-based
Stack machines are arguably the simplest kind of computer architecture. Their LIFO structure is quite suitable for block-oriented languages. The code size for a stack machine can be very compact because most instructions have no operand field.
Niklaus Wirth
Niklaus Wirth (born 1934 in Switzerland) is one of the most prominent computer scientists, mostly known for creating Pascal and several other programming languages.
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