Apologies for my "higgorance" if this has been asked (or answered) before - but - I've noticed that some of the Cargo 747's (Kalitta for example) with the longer upper deck "bulge" have seven windows visible on the port side, yet others (with the shorter "bulge") have only 3 windows.

Do the upper deck areas have space for passengers, or are they crew rest areas, or what?

It's intriguing me!

Any "gurus" out there know?

Have a great weekend all!