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I'm a little bit confused about Task Manager and usage memory.

Is the sum of all memory processes equal to the physical memory used?

This is a picture of my Task Manager ordered by memory usage high to low:

enter image description here

This is a screenshot of the physical memory used at the same time:

enter image description here

However, the sum of all the memory processes is less than the ~11 GB shown in the second picture.

Which is the true usage?

The OS is Windows Server 2003 Enterprise Edition 64-bit (running on a virtual machine with four CPUs and 24GB RAM)

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1  
Which OS version? It matters because the meaning of the "memory usage" column in taskmgr changes from release to release. –  Larry Osterman Feb 1 '12 at 14:28
    
"Is the sum of all memory processes equal to the physical memory used?" No. For example, if a process terminates but some of its pages hold useful information that might be used by another process, that physical memory remains used until the system needs it for something else. –  David Schwartz Dec 24 '12 at 14:37

3 Answers 3

There is an overlap in memory used by your applications. When an application is using a DLL, which is a shared library, the library is loaded into the physical memory only once, but every application using it sees an increase in its own memory usage. The Wikipedia article on shared libraries explains memory sharing quite well.

I see that your Windows is not in English, but if you try to translate the fields, I hope this information will help (taken from my Windows 7). The resource monitor can display working set, shareable memory and private memory for each process. Shareable memory and private memory are both combined into the working set of the application. Resident set is part of working set which is in physical memory (RAM) as opposed to being swapped on the hard drive.

So each shared library contributes towards the shareable memory of each application, which is a part of the working set. You have added up all working sets of all applications, I believe.

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Windows Vista and 7 will cache a certain amount of memory in case it needs to be used later. Thus, the total of all running processes can often be less than the memory actually being used. See techrepublic. As far as I know, Windows XP reported pretty much just actual usage.

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the system is windows server 2003 enterprise edition 64 bit –  ced Feb 1 '12 at 14:39
    
I can't find a good reference for how Windows Server 2003 behaves, but if you're looking for the actual memory usage, I'd recommend perfmon. –  Nick Martin Feb 1 '12 at 14:47

Memory that contains useful information (such as the contents of files) is used, even if it's not currently being used by any running process.

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