The internal address for memory in Windows XP is represented as:

In Windows XP, the internal address for memory is represented using a path that follows a specific format. The correct representation, which is denoted as "//physicalmemory," signifies that it is accessing a resource related to the physical memory of the system. This format illustrates the system's way of denoting certain resources related to memory management, and in the case of Windows, it indicates how to interface with system resources such as physical memory.

The other options, while they may appear to reference memory, do not align with the conventions used in Windows XP for representing memory addresses. For instance, "/dev/mem" is typically a UNIX file system path for accessing physical memory, which is not applicable in the Windows operating system environment. Similarly, "$PHYSMEM" and "\SYSTEM32\PhysicalMemory" do not accurately reflect the method used by Windows XP to represent internal addresses for memory situations. These alternatives might be more relevant in different operating systems or contexts, but they do not represent the correct way to access memory in Windows XP.