Mark Russinovich: In my first Pushing the Limits of Windows post, I discussed physical memory limits, including the limits imposed by licensing, implementation, and driver compatibility. This time I�m turning my attention to another fundamental resource, virtual memory. Virtual memory separates a program�s view of memory from the system�s physical memory, so an operating system decides when and if to store the program�s code and data in physical memory and when to store it in a file. The major advantage of virtual memory is that it allows more processes to execute concurrently than might otherwise fit in physical memory.

While virtual memory has limits that are related to physical memory limits, virtual memory has limits that derive from different sources and that are different depending on the consumer. For example, there are virtual memory limits that apply to individual processes that run applications, the operating system, and for the system as a whole. It's important to remember as you read this that virtual memory, as the name implies, has no direct connection with physical memory. Windows assigning the file cache a certain amount of virtual memory does not dictate how much file data it actually caches in physical memory; it can be any amount from none to more than the amount that's addressable via virtual memory.