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A), that does not allow parallelism, only concurrency. B), that is a description of all single threaded systems. "Event driven design" is euphemism for "bolted on async primitives to a single threaded language." Multi threading is a super-set of "event driven design", and a much more scalable one.

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Node is largely a reaction to advances in event multiplexing like kqueue and epoll. It was intended to be a scripting language bolted on top of a single-threaded concurrency model. This design-decision corresponds to the before unseen degree of callback hell that is Node's primary pain point.

Who would ever design a language to be concurrent but not parallel? Seems like a work of masochism.

It was intended for low latency services that mostly wait on I/O. These services don't compute enough to need parallelism. Especially when you can just fork another process or FFI to a C library with proper threading if you need it. It is necessary that they be concurrent but parallelism introduces a LOT of complexity beyond that.

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