pFn

PFN is an acronym that can refer to multiple concepts depending on the context. In computing, the most common meaning is Page Frame Number, a numeric index used by an operating system to identify a fixed-size block of physical memory.

Page Frame Number describes a unit of physical RAM at the level of memory management. In most modern systems, memory is managed in pages (often 4 KiB in size). The PFN serves as an index into the set of physical page frames, while the operating system’s page tables and memory management unit handle the mapping between virtual addresses and these frames. PFNs are used in tasks such as page allocation, page replacement, and page fault handling. In practice, a physical address can be derived from a PFN by combining the PFN with an offset within the page, with the exact calculation depending on the architecture and page size. The concept is central to how virtual memory systems isolate processes and manage RAM.

In software development, PFN is also a common naming convention for a pointer-to-function type, particularly in Windows and related C/C++ code. A PFN-type definition designates a function pointer used for callbacks, event handlers, or dynamically loaded functions. The specific syntax varies by codebase, but the pattern is to declare a type that represents a pointer to a function with a given signature, enabling flexible passing of functions as arguments.

PFN thus has at least two widely used meanings in technology: a memory-management index for physical RAM and a conventional name for a function pointer type in programming. Other uses may exist in different domains, but these are the primary technical senses.