whats happening to my binary file size?

[Israel via Digitalmars-d-learn]

I wasnt paying any attention to the file size of my binaries when
i started using D.

My first program is simple and compiles at 486kb, which honestly,
is kind of absurd but anyways, after i start adding other imports
it ran all the way up to 4.5mb.

what i want to ask is, what exactly is happening to my binary
when all i do is import various modules?