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Methods used to construct floors are; Nominal lumber 2X8, 2X10 or 2x12's etc., floor trusses, and engineered floor joists. 
Nominal lumber has pretty much faded away with the ease of installation and consistent quality of pre-constructed floor trusses and engineered floor joists. 
The strength, quality and flexibility of the trusses and joists make them the more popular choice.
They can be manufactured in different depths, normally 16 to 24 inches and any length to about 30 feet.
Picture is of typical floor truss installation at a floor truss girder. 
Note the hangers that hold the floor truss level with the girder truss. Floor trusses allow much greater flexibility to run the duct work, plumbing lines and other components of the home because of the open web design. A typical floor system with the duct work, plumbing and other components installed prior to insulation and drywall. The ends of the floor trusses on an interior load bearing wall braced with plywood panels to keep them from rolling.
On the exterior walls, a band of plywood is installed on the ends instead of the panels. Floor trusses and I-Joists delivered to the job site already built and ready to be installed. Typical I-Joist installation.
I-joists are more restrictive, because of their solid construction and require engineering to cut the holes to run the duct work, plumbing lines and other components. I-Joists or engineered floor joists are pre-manufactured in various sizes and lengths.
They provide a more silent floor system, because there are no joints or hardware that can flex and squeak. Decking located at a bathroom.
The black lines are applied at the factory and serve as guides for the screws or nails that are installed to secure the decking to the joists. The walking surface normally referred to as decking is typically 3/4 inch tongue and groove plywood or OSB that is glued and screwed or nailed in place.
Higher end and custom homes may have 1-1/8 inch decking. Decking prior to the flooring installation. image editing javascript ajax by VisualLightBox.com v5.4