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Page File usage when RAM is free

I'm a little confused. If you will note my attachment to this question, you'll see that my system is using about 600-700MB of Page File, when it quite clearly has well in excess of 2GB of System RAM free for use.

My understanding of the page file is that it is used as a storage location when RAM becomes full, and some space needs to be created in RAM for new data.

Is my understanding wrong? Am I interpreting the data in Task Manager incorrectly? Why? Why not?
And the root question, why would my system page off to disk if there is RAM free?

Maximum points for this one (500) for a detailed answer! Thanks.
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tigermatt
Asked:
tigermatt
2 Solutions
 
Dirtpatch-JenkinsCommented:
Virtual memory is created using a special file called a swapfile or paging file.

Whenever the operating system has enough memory, it doesn't usually use virtual memory. But if it runs out of memory, the operating system will page out the least recently used data in the memory to the swapfile in the hard disk. This frees up some memory for your applications. The operating system will continuously do this as more and more data is loaded into the RAM.

However, when any data stored in the swapfile is needed, it is swapped with the least recently used data in the memory. This allows the swapfile to behave like RAM although programs cannot run directly off it. You will also note that because the operating system cannot directly run programs off the swapfile, some programs may not run even with a large swapfile if you have too little RAM.

So once something is stored in the pagefile it stays until it gets "pushed" out when needed.
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tigermattAuthor Commented:

Thanks for your description. However this is occurring pretty much after starting the system and without loading too many intensive applications. If I watch my Physical RAM usage, it never drops to a level whereby the OS is 'running out' and needs to page.

Is there some special level or % which the OS will try to keep in free RAM?
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Malli BoppeCommented:
nice question Tigermatt have seen this before but never thought of asking here.Want to see what the experts would come up with.
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Dirtpatch-JenkinsCommented:
Well, paging isnt a straight forward proposition...there are around 5 different ways that a system can handle "page faults".  

Demand paging - no pages are brought to ram until necessary.with demand paging, a program usually begins execution with none of its pages pre-loaded in RAM.

Anticipatory paging - preloads a process's non-resident pages that are likely to be referenced in the near future

Loader paging - guesses that the entire program will be used

and a few subsets.

so some programs load into page file even if you have a lot of free ram, and even more load what the system perceives will be little  used aspects into page file for recall if needed yet still keeping resources free
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Dirtpatch-JenkinsCommented:
And of course, it does this for a reason... it tries to anticipate loads...

say your running your browser, which is not a heavy load.. the system may page files for use later..

you decide to kick on your dreamweaver and visual basic at once...well more ram is free to handle that because paging was utilized properly to begin with,, rather than things having to be swapped on the fly.
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Dirtpatch-JenkinsCommented:
You can visualize it like the windows OS itself... Its running on the .net framework - all kinds of functions are partitioned off into dll's  , when a procedure needs to do  "x" it calls on the appropriate .dll.

If the OS had to load all the functions held in the various .dll's it would be a behemoth.

So the paging file is used even when ram is free for much the same reasons,, kind of a load balancing to maximize available resources.
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PCBONEZCommented:
>> without loading too many intensive applications <<

XP -is- an intensive application.

What Dirtpatch said is right.

Additionally, have you ever noticed some page [usually a web page] you had minimized in back sort of 'hang' at first when you maximize or bring it up front again? [Good example is scroll won't work right away.]
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What happens is that page is sent to virtual memory because it isn't active and the hang occurs while  waiting for it to 'get back' from the virtual memory on you hard drive and into physical RAM again.
.
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tigermattAuthor Commented:
Thanks guys. So essentially, what we are saying here, is it is perfectly normal for my Page File usage to be up around 600MB after starting my PC?
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Dirtpatch-JenkinsCommented:
Yes,, perfectly.
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