Virtual memory, page file in 64bit system

[Octopuss]

I was thinking a little. There are hundreds of wannabe tweaks for Windows systems, one of them being classical "myth" about disabling the page file completely. The argument against that is more or less like this (no idea where I found it anymore):

Myth - "Disabling the Paging File improves performance."

Reality - "You gain no performance improvement by turning off the Paging File. When certain applications start, they allocate a huge amount of memory (hundreds of megabytes typically set aside in virtual memory) even though they might not use it. If no paging file (pagefile.sys) is present, a memory-hogging application can quickly use a large chunk of RAM. Even worse, just a few such programs can bring a machine loaded with memory to a halt. Some applications (e.g., Adobe Photoshop) will display warnings on startup if no paging file is present."

Notes - "In modern operating systems, including Windows, application programs and many system processes always reference memory using virtual memory addresses which are automatically translated to real (RAM) addresses by the hardware. Only core parts of the operating system kernel bypass this address translation and use real memory addresses directly. All processes (e.g. application executables) running under 32 bit Windows gets virtual memory addresses (a Virtual Address Space) going from 0 to 4,294,967,295 (2*32-1 = 4 GB), no matter how much RAM is actually installed on the computer. In the default Windows OS configuration, 2 GB of this virtual address space are designated for each process' private use and the other 2 GB are shared between all processes and the operating system. RAM is a limited resource, whereas virtual memory is, for most practical purposes, unlimited. There can be a large number of processes each with its own 2 GB of private virtual address space. When the memory in use by all the existing processes exceeds the amount of RAM available, the operating system will move pages (4 KB pieces) of one or more virtual address spaces to the computer's hard disk, thus freeing that RAM frame for other uses. In Windows systems, these "paged out" pages are stored in one or more files called pagefile.sys in the root of a partition. Virtual Memory is always in use, even when the memory required by all running processes does not exceed the amount of RAM installed on the system."

Allright. Naturally, in 64bit system things are a bit different. Can anyone put a bit of light on this? How much different the situation is etc.?

Edited May 18, 2009 by TheWalrus

[cluberti]

Well, although layout of the application and kernel VA is larger, you still have the same APIs for memory allocation and management so the same sorts of logic apply. Obviously the amount of RAM in a system changes the numbers a bit, and depending on the app load the box runs, you likely still need a paging file, and perfmon analysis of a running system can tell you how best to tweak it.