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Cached memory query

Running Windows 2008 Server (VM). The guest has been allocated 4GB RAM.

If I go to the Task Manager, I can see the following:

Physical memory (MB)
Total: 4094
Cached: 2456
Free: 74

The memory level picture in Task Manager shows 3.53 GB memory used.

Does this mean the machine is running out of memory? What does the "cached memory" actually do, is it being used or free?

And how does this fit in with page file usage? The page file is on the C: drive and has 5GB.
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neil4933
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neil4933
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Frosty555Commented:
For your purposes you can consider the cached memory to be "free".

Here's an example of Task Manager on one of my servers, a domain controller that is very lightly loaded for the amount of horsepower it has:

Task Manager
You can see the server has 12GB of memory. Yet it has 0MB free. In this case, the "Available" memory line item is what is telling the real story - the server has allocated all of the memory on the server but it is only using about 1.92GB of it.

Resource monitor gives a better picture without getting too deep into the specifics:

Resource Monitor
In reality only 1.9GB is actually in use. The rest is cached and in standby, but should basically considered to be free memory.


Regarding your swap file - for your purposes you can consider it to be unrelated to the rest of your memory situation, it is not being used in the calculations you posted in your question. It is just reserve memory in case the server runs out. Old or infrequently used pages of memory are swapped out into that file so that faster RAM can be used for more important things.

If the computer gets sufficiently low on memory that it actually has to start using the pagefile heavily, you'll know about it. The whole server will grind to a halt and you'll have severe performance issues.
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neil4933Author Commented:
Hi Frosty

Thanks for the great explanation, really appreciate that :-)

So you would say that cached memory is actually "free" memory?

And the Memory/ Available Mbyes in Perfmon, is that a reliable counter to use in Perfmon, i.e. if it falls beneath 5-10% of the total RAM should we be worried, or does other factors like PAging coming into this?
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Frosty555Commented:
For the purposes of deciding if the server has adequate memory, the Available MBytes is reliable. Paging is an important metric, but it tells you different information.
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