HP-UX 11i Internals

Address Translation

Address translation is the process of translating a virtual address to a physical address. Before we begin the translation process, the virtual address is divided into a virtual page number (VPN) and an offset into that page. The VPN is then translated into a physical page number (PPN), and the offset is used as the offset into that physical page.

In PA-RISC 1.1, all pages are a fixed 4 KB long. This means that the offset portion of a virtual address is the lower 12 bits, and the VPN is the upper 20 bits. With PA-RISC 2.0, we introduced the concept of variable-sized pages. This means that the physical pages can be from 4 KB to 64 MB. However, for the purposes of address translation, we assume a 4-KB page size. Thus, we still ...