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Whenever I press NumLock key, a small LED on desktop tower blinks once. Can someone explain it why this happens ? The led has symbol which looks like a battery or disk.

Edit: LED does not blink when I press capslock or scroll lock. This happens in Ubuntu only. While using Windows led doesn't blink.

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    CPUs don’t have LEDs. What are you referring to? Perhaps the PC case?
    – Daniel B
    Commented Oct 3, 2019 at 11:32
  • @Daniel B I will share a video for more clarity.
    – K_peanutButter
    Commented Oct 3, 2019 at 11:34
  • Does it blink immediately or does it blink e.g. exactly a second later or so?
    – grawity_u1686
    Commented Oct 3, 2019 at 11:35
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    By "CPU" he means the desktop tower itself. For some reason, lots of people call a desktop PC a "CPU". The LED is the hard drive activity LED. When he enables/disables Num Lock, the computer briefly accesses the hard drive.
    – Mr Ethernet
    Commented Oct 3, 2019 at 11:40
  • @wrecclesham thanks for pointing out. I have edited the question. Since the school time teachers have been teaching us "it is called CPU".
    – K_peanutButter
    Commented Oct 3, 2019 at 12:01

1 Answer 1

Reset to default
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Most likely option: Windows records your NumLock preference in the Registry, and then flushes the Registry change to the disk (updating the NTUSER.DAT file).

However, you can use ProcMon to check what actual activity is happening. (Note that it might generate disk activity on its own, and you might need to exclude a lot of processes before you can see anything useful.)

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  • That's interesting. I always thought it would only need to exist in RAM because the Num Lock state doesn't persist between reboots.
    – Mr Ethernet
    Commented Oct 3, 2019 at 11:42
  • Maybe I'm confusing this with another OS which did store it persistently?
    – grawity_u1686
    Commented Oct 3, 2019 at 11:45
  • I know in the BIOS you can usually specify the Num Lock status at boot but I'm not sure if it's effectively Yes/No or Yes/last state remembered by Windows. I'll experiment and see how it works on my PC.
    – Mr Ethernet
    Commented Oct 3, 2019 at 11:49
  • On my parent's Windows 10 laptops the state of NumLock is surely persisted between reboots (and after a full power down). I doubt it's the laptop/external keyboard itself that is doing that, but maybe it is.
    – Arjan
    Commented Oct 3, 2019 at 12:01
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    Because Caps Lock and Scroll Lock are not persisted (it doesn't make much sense to persist them from usability point of view).
    – gronostaj
    Commented Oct 3, 2019 at 12:39

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