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Quad core only showing three in Task Manager.

    Question

  • Just a few days ago, all four cores were showing up. I had encountered a similar issue on another computer (that has Hyper-V running on it) where one core was missing. Turns out that somehow, one of the cores was turned off in the BIOS. I fixed that and everything is fine on it. NOW, on my main computer (ASUS M3N78-EM, BIOS 0704, AMD X4 965, it's a quad core), the normally 4 cores that show when I use the Affinity option for a task is now only showing 3. The BIOS reports 4 cores and the Device Manager shows 4 processors. However, the Task manager only shows 3, the NUMBER_OF_PROCESSORS value via the command line shows '3', in RegEdit, only '3' and when I try to use MSConfig, advanced options, it only lists 3 cores. I've tried changing the value in the registry to '4' and doing a reboot. Didn't work. Also looked in the BIOS and can't find anywhere that lets me decide how many cores to use (ie, if I want to disable a core or something, so I could see if it somehow got triggers). No good. Even tried setting the value via the command line and that doesn't have any effect (not that I really thought it would, but had to try anyway to see if it would help at all. I believe I may have somehow messed it up a few days ago (read first part of this post) by somehow limiting the maximum number of cores that W7 will see. Now I just need to somehow undo that, preferably without seeing if I can do a system restore (not sure if I have any I can revert to, to be honest). So am I missing something? Is there someplace else that I'm not aware of that helps to control the number of cores that the system has access to? I'm going to keep trying a few things, so obviously going to have several reboots (which I dread). Just hope there's a simple solution, without doing a fresh install.
    Monday, January 16, 2012 12:58 AM

Answers

  • No, not a problem with the CPU. I've got 4 again and I think I know why, although there are two possibilities. First, I uninstalled each of the cores via the Device Manager. Uninstall and then when you start back up, it reinstalls right? (Well that's what it did for me at least.) Could be that it cleared something up. Or, second possibility, and I believe this is what happened to me. I think I had diddled with MSConfig and had set and even saved the setting of only having 3 cores available. Without restarting, unchecked the option to specify the number of cores. My theory is that the first save is what took, so it limited the number of cores. However since I had unchecked the option, it updated that part but not the fact that it wasn't supposed to limit the number of cores. Deciding to at least enable, reboot, disable, reboot to see if it would help, I limit the number of cores to two. Reboot. Disabled the option. Reboot. Now the number of cores is restored to four. It could still be from the first one though, as a reboot will reinstall the drivers for the processors and then tell you that you need to reboot. Or could be a mix of the two. Either way, have all four cores available again. I'll probably be doing a few more reboots in the next day or so, so will try to take a few minutes to test the theory out (the second one that is).
    • Marked as answer by Fangs McWolf Tuesday, January 17, 2012 8:55 AM
    Monday, January 16, 2012 1:25 AM

  • Download and install CPU-Z  http://www.cpuid.com/softwares/cpu-z.html  . How many cores does it show?

    As VF stated, it's possible that one core died; that's not unheard of. You really can't go by what the BIOS says; I can set my x2 to 6 cores, but only 4 show in Windows (ASUS m4n68t-m v2, AMD Phenom II x2 555). Try limiting your CPU in BIOS to the core 0 + one other core, then look and see in Windows what is showing (if your MB BIOS has that ability). I don't know of any core-testing utilities to see if one's dead or not, but there may be some out there. Google, maybe?


    SC Tom


    Nevr mind- I see you figured it out :-)
    • Edited by SC Tom Monday, January 16, 2012 2:08 AM
    • Proposed as answer by Miya YaoModerator Tuesday, January 17, 2012 8:29 AM
    • Marked as answer by Fangs McWolf Tuesday, January 17, 2012 8:55 AM
    Monday, January 16, 2012 2:05 AM

All replies

  • No, not a problem with the CPU. I've got 4 again and I think I know why, although there are two possibilities. First, I uninstalled each of the cores via the Device Manager. Uninstall and then when you start back up, it reinstalls right? (Well that's what it did for me at least.) Could be that it cleared something up. Or, second possibility, and I believe this is what happened to me. I think I had diddled with MSConfig and had set and even saved the setting of only having 3 cores available. Without restarting, unchecked the option to specify the number of cores. My theory is that the first save is what took, so it limited the number of cores. However since I had unchecked the option, it updated that part but not the fact that it wasn't supposed to limit the number of cores. Deciding to at least enable, reboot, disable, reboot to see if it would help, I limit the number of cores to two. Reboot. Disabled the option. Reboot. Now the number of cores is restored to four. It could still be from the first one though, as a reboot will reinstall the drivers for the processors and then tell you that you need to reboot. Or could be a mix of the two. Either way, have all four cores available again. I'll probably be doing a few more reboots in the next day or so, so will try to take a few minutes to test the theory out (the second one that is).
    • Marked as answer by Fangs McWolf Tuesday, January 17, 2012 8:55 AM
    Monday, January 16, 2012 1:25 AM
  • I use a few command line programs (like exf.exe) and sometimes I need to limit its priority, but not by priority but rather affinity. So I go in and give it access to only one or two cores, so that other things continue to function properly.  I generally don't go changing the affinity of things like, oh, say, wininit.exe or winlogon.exe or something.
    Monday, January 16, 2012 1:59 AM

  • Download and install CPU-Z  http://www.cpuid.com/softwares/cpu-z.html  . How many cores does it show?

    As VF stated, it's possible that one core died; that's not unheard of. You really can't go by what the BIOS says; I can set my x2 to 6 cores, but only 4 show in Windows (ASUS m4n68t-m v2, AMD Phenom II x2 555). Try limiting your CPU in BIOS to the core 0 + one other core, then look and see in Windows what is showing (if your MB BIOS has that ability). I don't know of any core-testing utilities to see if one's dead or not, but there may be some out there. Google, maybe?


    SC Tom


    Nevr mind- I see you figured it out :-)
    • Edited by SC Tom Monday, January 16, 2012 2:08 AM
    • Proposed as answer by Miya YaoModerator Tuesday, January 17, 2012 8:29 AM
    • Marked as answer by Fangs McWolf Tuesday, January 17, 2012 8:55 AM
    Monday, January 16, 2012 2:05 AM
  • Even though your post wasn't an actual answer, I marked it as one anyway, since the CPU-Z tool (which I've used before) can be VERY helpful for troubleshooting an issue like this.

     

    If someone else stumbles on this with the same problem, it could help them out.

    Tuesday, January 17, 2012 8:57 AM