What is ID of the root ( / ) Site?

How safe is it to assume that the root or “/” blog id using the ID of “1”? I’ve created and deleted entire sites and installations trying to see if “/” could be made to have an id other than 1 — but just because I haven’t been able to make it happen doesn’t mean it can’t happen.

If it’s not a safe assumption, do you have any suggestions for identifying “/” and retrieving that ID?

For the curious, I’m working on my first Multisite aware plugin and I’ll need to know when the main site is making a post, or when it is any of the sub-sites. I may also need this id for queries and/or switch_blog().

Thanks for the help.