I basically think of a single computer as a distributed system now. In other words, it's not a Turing machine / state machine any more; it's a network of such

I basically think of a single computer as a distributed system now. In other words, it's not a Turing machine / state machine any more; it's a network of such things. Once you have multiple CPUs, you can't avoid concurrency, and message passing and immutability become common themes. The strategy for many years was to naively add locks to traditional stateful algorithms and mutable data structures, but this often leads to bad performance (and unpredictable performance) There is an elaborate backward compatible illusion presented by the architecture, C, and most languages built on top of C. Internal busses and caches are not exposed to you as a programmer, but they are there and affect performance. But if you think of your app from the OS perspective rather than the language perspective, the distributed model becomes more clear and natural.