Windows NT Virtual Memory Manager Uses FIFO

ID: Q98216

3.10 3.50 3.51 4.00 WINDOWS NT kbprg

The information in this article applies to:

Microsoft Win32 Application Programming Interface (API) included with:
```
    - Microsoft Windows NT versions 3.1, 3.5, 3.51, 4.0
```

On page 193 of "Inside NT," Helen Custer states that the Windows NT virtual memory manager uses a FIFO (first in, first out) algorithm, as opposed to a LRU (least recently used) algorithm, which the Windows virtual memory manager uses. While it is true that FIFO can result in a commonly used page being discarded or paged to the pagefile, there are reasons why this algorithm is preferable.

Here are some of the advantages:

FIFO is done on a per-process basis; so at worst, a process that causes a lot of page faults will slow only itself down, not the entire system.
LRU creates significant overhead--the system must update its page database every single time a page is touched. However, the database may not be properly updated in certain circumstances. For example, suppose that a program has good locality of reference and uses a page constantly so that it is always in memory. The operating system will not keep updating the timestamp in the page database, because the process is not hitting the page table. Therefore this page may age even though it is in nearly constant use.
Pages that are "discarded" are actually kept in memory for a while, so if a page is really used frequently, it will be brought back into memory before it is written to disk.

Additional reference words: 3.10 3.50 3.51 4.00 KBCategory: kbprg KBSubcategory: BseMm

Keywords          : kbAPI kbKernBase kbGrpKernBase 
Version           : 3.10 3.50 3.51 4.00
Platform          : NT WINDOWS

Last Reviewed: December 22, 1996