>http://www.itworld.com/article/2901453/no-its-not-always-quicker-to-do-things-in-memory.html

This only means that high level languages do a lot work on that specific task

The data was just witten to disk (Possibly as fast that it was just a change to the write cache or name it buffer.) IOW write to a pretty well allocated memory block

The lang otoh was just allocating and reallocating over and over

Or one can say the allocating mechanism of the buffer is better / faster implemented then that of the lang. So the fastest way to concenate a string is: Concenate to disk buffer, read from buffer, delete from buffer :)