The page register selects between up to 256 NVEM pages. Each page will usually be the totality of a particular NVEM type. The default page is 0, and corresponds to selecting the type 0 NVEM. In 99% of applications only page 0 will ever be used, as it is the one page that we expect to exist in all future (post 1Q05) SPLat products.
The remaining registers act on the NVEM within the selected page.