Index Allocation Maps I am a developer reading the book "Querying Microsoft SQL Server 2012." I have come across the following diagram:




Why are the pages in the first two rows of the diagram (row 1 starting: 1:174 and row 2 starting: 1:41) not part of an extent? The documentation says: "all pages are stored in extents": 
How does the number scheme work e.g. what does 1:174 mean?
Directly above the diagram, the book says: "IAM pages for an object are organized as a doubly linked list;"  The diagram does not show any links between the pages.
They are part of a mixed extent, the diagram just didn't draw a grey box behind them, probably more to keep it from being too busy as much as anything.
Data File : Page
Again, I think this is just meant to simplify and not make the diagram too busy, as well as not give any sort of suggestion that pages will necessarily be linked in a certain order. Surely you can picture the arrows that would represent a doubly-linked list? 


For most of this, you're much better off asking the author of the book and creator of the diagram, than a community of peers.