The original incarnation of pfdat was quite simple. Each page had a pfdat structure, and the entries were arranged in a simple array. The physical page frame number served as the index into the array. As we mentioned in our discussion of the pfn_to_virt_ptr structure, modern HP-UX systems must be able to handle partitioned memory configurations. With the advent of today's cell-based systems with their physical and virtual partitioning schemes, this requirement is coming under a new focus. Figure 6-14 illustrates the current incarnation of the page free data table.