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In Windows Task Manager and AVG Task Manager (included in TuneUp Utilities), I see that the sum of all the running processes is much lower than the total CPU usage shown in "performance" tab. Does this mean that my PC is running a hidden process or some malware that's not displaying in the Task Manager?

EDIT: inbuilt monitor showing this too, and show processes from all users showing too. laptop is two-cores, and I'm taking total load of both.

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  • Interesting queston, did you take load per core and hyperthreading into account ? I'm not sure if a keylogger would be that obvious to notice.
    – Saint Crusty
    Commented Sep 21, 2014 at 18:26
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    How large is the difference? If it's not too big (relative to the total number of processes), it could easily be from the fractions of a % adding up.
    – Kitsune
    Commented Sep 21, 2014 at 20:33
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    Is there a "Show Processes from All Users" button? Sometimes the windows task manager will hide system processes if you don't click the button.
    – user54791
    Commented Sep 22, 2014 at 1:34
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    In addition to the comment above about showing all users processes, it could well be hardware interrupts, which task manager doesn't show. You'd be better using the built in resource monitor, by opening task manager, going to "Performance" and clicking on resource monitor.
    – Chris Murray
    Commented Sep 22, 2014 at 7:59
  • You would need to run a facility that explicitly takes into account the CPU usage of the kernel and other users. I don't know Windows well enough to know whether the Task Manager does that for you out of the box but you ought to check. For the matter a keylogger is such a trivial piece of code that it should not consume any noticeable amount of CPU.
    – Steve DL
    Commented Sep 22, 2014 at 16:55

5 Answers 5

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This is because the task manager round up or round down the CPU usage values per process. You can see a lot of process using "0" CPU time, this is false, they use "0,xxxxxxx" cpu time.

What you need is a process manager showing more precise value to you.

Some process can also be hidden (negative PID, running as another user) or some piece of hardware may have direct access to the CPU by passing your operating system (but probably not)

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    negative PID? how can I view processes with negative PID?
    – tensojka
    Commented Sep 29, 2014 at 16:57
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    This is another question and should have it's own question page. If my answer is correct about the specific question you asked you can mark it as answer with the checkmark icon. You could ask "How to list process with negative PID on Windows" on the new question page.
    – Zulgrib
    Commented Sep 30, 2014 at 18:54
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    There is no such thing as a "negative PID" in Windows. PIDs are not signed numbers, at all.
    – Jamie Hanrahan
    Commented Aug 1, 2015 at 20:40
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    Thanks for your input, this explains why security software actively track process with negative PID. support.kaspersky.com/6658 Have a nice day.
    – Zulgrib
    Commented Aug 2, 2015 at 9:19
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    I don't think this is caused by rounding error. On my system, there is one process showing 6% in Task Manager, while the same process shows 10% in Process Explorer. This accounts for the difference, although I don't know why.
    – Elliott B
    Commented Sep 2, 2020 at 19:13
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Run Process Explorer and you'll see the cpu usage for everything including services like anti-virus checkers. (I just had the same issue and I found Symantec's ccSvcHst.exe was taking up 13% of my cpu.)

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  • I came here because it seemed like Symantec was gobbling up my CPU too.
    – Brock Brown
    Commented Oct 30, 2023 at 11:42
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I doubt that "much lower" is due to rounding errors.

I assume you see the same bug as I often see, where the process list does not update properly, so when I start some job taking a decent amount of cpu power, like a compile or similar. Then it happen from time to time that this new process is not added to the list by task manager.

I found that switching to another tab (ex. "performance") and then back to the "processes" tab, triggers a rinse and repeat of the list, making my new process show up in the list.

And now the sum matches the reported total way better.

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  • This really helps! After a switch to Performance and back to Processes, it updates and I can see some processes that eat the CPU! @tensojka, I guess, this is the correct answer, not "rounding up" answer
    – shal
    Commented Mar 19, 2021 at 0:12
  • This didn't work for me (2012R2), but F5 did. At that point I realised it was because the Update Speed was set to Paused.
    – mwfearnley
    Commented Jun 15, 2022 at 15:42
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I had the same issue, where the built in task manager recorded a CPU usage much higher than the processes I was running.

Using Process Explorer, I found that the process using up my CPU was a image editor that was running on another Windows user.

Switching to that user, logging out and then logging back in to the first user confirmed that the CPU was now down to expected levels.

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process explorer screenshot

i've attached a screenshot, from process explorer. Simply looking at the CPU usage graph it is obvious that the ~85%ish usage the graph shows is more than the sum of CPU usage added up in the listed processes.

My assumption is that the CPU is doing I/O functions that have no processes.

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    – Community Bot
    Commented Sep 30, 2023 at 18:29

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