A page table is simply an array of 32-bit page specifiers. A page table is itself a page, and therefore contains 4 Kilobytes of memory or at most 1K 32-bit entries.
Two levels of tables are used to address a page of memory. At the higher level is a page directory. The page directory addresses up to 1K page tables of the second level. A page table of the second level addresses up to 1K pages. All the tables addressed by one page directory, therefore, can address 1M pages (2^(20)). Because each page contains 4K bytes 2^(12) bytes), the tables of one page directory can span the entire physical address space of the 80386 (2^(20) times 2^(12) = 2^(32)).
The physical address of the current page directory is stored in the CPU register CR3, also called the page directory base register (PDBR). Memory management software has the option of using one page directory for all tasks, one page directory for each task, or some combination of the two.