Node output formats

I can't seem to find any info on what a noise node (just for example) puts out. I always assumed it was random between 0 and 1  but in trying a simple OSL shader it SEEMS to be mostly somewhere between .5 and .6

I'm trying to follow  "Open Shader Language for Blender"  by Michel Anders. I have no trouble following code but when you can't see the input format it's more than a problem. 

And this goes for other types of nodes.

The manual is mute. Even a graph of the output would be helpful.