However, before I continue to write about the paper, I should give a short explanation of Turing complete languages and why these are important: In 1937, a few years before the first programmable computer was built, the mathematician Alan Turing invented the concept of a Turing machine to prove that a universal (or programmable) machine can be built that can solve any computable problem. Although no universal Turing machine will ever be built since it requires infinite memory, this is basically the most important result of computer science. If you take a set of instructions which are sufficient to simulate such a Turing machine (with exception of the infinite memory), this set is called "Turing complete". This certainly is not the biggest deal in the world since all modern processors have Turing complete instruction sets. And indeed, in both papers, the Turing completeness of the languages is only used to prove that their languages do not lack fundamental concepts.
So let me now explain what's so special about the language introduced in "Platform-Independent Program". Commonly the instruction sets of two different processors overlap to a certain extent but are not equal; a program for x86 processors will never run on an ARM processor and vice versa. So the authors of the paper started looking at the overlap of the instruction sets to find jump instructions that will have the following effect:
- If executed on platform a, jump to address x.
- If executed on platform b, jump to address y.