Why do Resource Monitor and Task Manager's total RAM usage not even remotely add up to the total Physical Memory usage?

I have noticed this on many different Windows machine, on many different occasions: the RAM usage reported by Task Manager or Resource Monitor often seems to add up to an amount which is significantly lower than the actual amount in use.

For example, many times on my laptop or my desktop, I have seen something like 7GB in use, and yet the total of the Working RAM Set is more like 3GB. I just can't figure out where it's being used!

Here's an extreme example I noticed today in Resource Monitor on a server:

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If you right-click the image and open in a new tab, and view the numbers, you'll notice that the Working Set (which doesn't include nonphysical virtual memory) add up to about 1.7GB. I get similar numbers by adding up RAM usage in Task Manager when "Show processes from all users" is enabled.

Now here's a screenshot of task manager's Performance tab:

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This says 7.6GB of physical memory is in use.

I see this all the time, on personal computers, laptops, and now servers: the total RAM usage reported by system tools only accounts for about 1/4 of the RAM usage I observe. WTF is going on???

Is there any satisfying explanation of where all my RAM is? What is gobbling it up, and why is it leaving no trace?

EDIT: Here's a picture of the graphical RAM use, as user whs asked for:

^{Click for full size}

EDIT 2: In response to James' response, here's a picture of the nonpaged processes in poolmon.exe, sorted by size:

These results confuse me. poolmon correctly states that I have 6GB of nonpaged pool in use, but all the nonpaged pool processes are less than 8MB in size.

What could this mean? Is poolmon failing to detect some of the processes using the nonpaged pool?

Answer

I'm sorry, I know this sounds like a flippant response... but the answer to the question in your title is "because they're not supposed to."

Or to put it more politely: There is much use of RAM that is not in processes' private working sets. Some of it is in processes' shared working sets - but you can't get a reliable notion of the actual usage there, because of sharing; adding up the processes' numbers will give you far too large a result.

Other stuff that occupies RAM, like the nonpaged pool, the resident portion of the paged pool, and the resident portions of other kernel-space uses, doesn't show up in Task Manager's "processes" display at all.

Regarding your specific issue:

On the Task manager display, see the "kernel memory" section? You have 6 GB of "nonpaged memory" (that's nonpaged pool). That's part of the "In use" section in your second graph. The nonpaged pool is not charged to any process, which is why adding up the per-process numbers in task manager doesn't get close to the total in use. Some driver is most likely using it. This is a wholly excessive amount; it should be well under 1 GB. whatever driver is responsible for the excessive part of the nonpaged pool usage is unquestionably buggy.

RAMmap can confirm this (on its "Use Counts" tab, look at the total for "Nonpaged Pool") but it can't help you find which driver is causing it.

Here's how to find it: Obtain a copy of the Microsoft tool "poolmon". It is a character-mode tool (boy, is it ever) distributed with the Windows Driver Kit. For Windows 7 the WDK is a free download. You have to download the whole thing (it's an ISO) and install it from that, but you can choose to install just the tools, if that's all you want.

Find poolmon in the WDK directories - be sure to pick the right one, 32- or 64-bit - and run it from an administrator command prompt. You will get a display like this:

Now, press the "p" key (no, I'm not kidding. No menus here!) until the "Type" column shows only "Nonp". Then press "b" (twice if necessary) to sort the display in descending order by the Bytes column (that was already done in the sample here).

Then look at the "Tag" column for the topmost line. In the (obviously artificial) case shown here it's "Leak". (This system is running a driver that was deliberately bugged to cause this problem- it's "leaking" nonpaged pool.)

btw, the highlighted lines are the ones that changed since the previous update to this archaic screen.

Now search c:\Windows\System32\Drivers for a .sys file containing that string. In this case you'd be looking for "Leak", like this:

c:\windows\system32> findstr /s Leak *.sys

Then search the web for references to that string and/or that driver name.

Returning here and reporting the full name, manufacturer name, etc. from the .sys file would be helpful too.

(My bet is that the tag you find will be ECMC, the driver is intmsd.sys, and it's associated with a product called ExpressCache or IntelliMemory. I would "uninstall" that product. There is an update to fix the problem, but even with the fixed version I have never seen a system's performance improved by this product; it essentially duplicates functionality that's already in Windows.)

If you can't find it that way, the next step is to use the "Windows Performance Toolkit". Search this forum for that string, with answers by magicandre1981, for a how-to. Ignore answers that mention xperf - it is an older version of the tool.

UPDATE: Per the comments, the OP did the above and found that though poolmon reported the total size of the nonpaged pool was indeed huge, all of the allocated pieces were apparently tiny. My conjecture (also in the comments) is that this is due to what I will call "bloated" pool: Pool was allocated, then freed, but for some reason that amount of RAM allocated to pool was not shrunk to reflect the "freeing". Following the procedure described in this answer by magicandre may identify the culprit.