I've actually used an STL port to Arduino and was able to create a standard vector of length three but not four. that crashes the system.

I believe it uses a custom allocator.

Actually Arduino code does tend to use dynamic allocation for things like strings - it's a lot easier than the alternative, they tend to have quite a lot of memory these days (e.g. 1 MB) and hobby projects don't need to be super-reliable usually.

One megabyte or ten isn't enough to bother with mapping, and on Arduino you don't typically have memory mapping hardware anyway. "Big" means gigabytes these days, sometimes hundreds of them.

but often you might write code that you dont know it will end up there, like lib