Osb oriented strand board is a different form of sheet material.
Best attic subfloor.
The most common uses are as sheathing in walls flooring and roof decking.
Plywood or chipboard is the least expensive option for storage flooring.
Weight concerns if you do have an existing walk up attic with traditional floor framing the principle concern when converting the space into a living area will be weight.
Plywood is familiar to most people it is a sheet material made from layers of wood oriented in opposite directions from layer to layer.
The decision regarding the thickness of plywood to use for the subfloor in the attic has a lot to do with how you intend to use the attic and it also depends on the spacing of the ceiling joists.
Since the boards are sold in 4 foot by 8 foot sheets you may need to cut them into 2 foot wide strips to get them into the attic space.
The best you can hope for is perhaps to lay some thin plywood platforms down over the bottom truss members and use them to store lightweight items.
The wood should be at least 5 8 inch thick to handle a heavy load.