I have noticed that when pressing keypad numbers (not standard keyboard numbers) while num-lock is disabled, the computer is receiving some sort of input/data.

On Windows 7, at the log-in screen, the cursor moves from the password field to other fields.

In software running on a Win7 machine the cursor flashes.

I am curious as to what info the computer is receiving. Before encountering this behavior I would have posited that the computer would simply ignore any input whatsoever; but this does not seem to be the case.

  • 1
    I must be missing the question. If you're referring to the number pad, that has two sets of inputs printed on the keys, numbers and navigation functions. The Num Lock selects which is used, like the Caps Lock key selects upper vs. lower case characters on the regular keys. – fixer1234 Jul 6 '16 at 16:48
  • I suspect you don't know what a CPU actually is. It might be helpful to punch "CPU" into your favorite search engine and follow a link or two. – David Schwartz Jul 6 '16 at 19:06
  • Modified title to reflect the more semantically correct OS vs CPU. – iAndelin Jul 6 '16 at 19:14

What info/data is sent to the CPU when pressing keypad numbers

When you press any key, a scancode is sent to the motherboard.

When you release that key, a different scancode is sent.

with num lock off?

The state of num-lock has no effect on what is sent from keyboard to motherboard. It only affects how your operating system interprets the meaning of the scancodes.

Some keyboards have some local intelligence built in, these may not send scancodes under some circumstances (e.g. built-in calculator, toggle games modes, etc).

Most basic keyboards do not. For example, you may have noticed that when you press (and release) Num Lock a LED indicator light goes on or off. The state of the LED is not controlled internally by the keyboard itself. This is why it is a useful test of your keyboard's connection to the motherboard and of the healthiness of your operating system.

while num-lock is disabled ... the cursor moves from ... field to other fields.

That's because the numeric keypad is normally labelled like this.

enter image description here

If the OS thinks num-lock is on, the scancode from releasing 6 is interpreted as a digit 6. If the OS thinks numlock is off, the same scancode, from releasing 6, is interpreted as ⇨ right-arrow (move cursor right)

So num-lock† acts like a kind of shift-lock for the numeric keypad. It causes the function of the numeric keypad to toggle between numbers and cursor-movement. It is not intended as a way of completely disabling the numeric pad.

†More accurately, the OS chooses to interpret the scancode sent by releasing Num-Lock as switching to an alternative set of interpretations of the scancodes sent when numeric keypad keys are released.

  • 1
    +1 for the very literal interpretation of the question! – FreeMan Jul 6 '16 at 17:09
  • 1
    @FreeMan: :-) I added some more helpful details, but I kinda like being literal. – RedGrittyBrick Jul 6 '16 at 19:10
  • That was thorough. – user477799 Jul 6 '16 at 19:11
  • A nitpick with "The state of the LED is actually controlled by the motherboard" as AutoHotkey can bind NumLock to arbitrary action, without toggling the LED. – guest-vm Jul 7 '16 at 15:33
  • @guest: thanks. I have edited the answer rather than nitpick the nitpick :-). – RedGrittyBrick Jul 7 '16 at 15:38
NumLock ON  NumLock OFF   ON/OFF Effect
Numpad0     NumpadIns     0 / Insert key
Numpad1     NumpadEnd     1 / End key
Numpad2     NumpadDown    2 / Down arrow key
Numpad3     NumpadPgDn    3 / Page Down key
Numpad4     NumpadLeft    4 / Left arrow key
Numpad5     NumpadClear   5 / typically does nothing
Numpad6     NumpadRight   6 / Right arrow key
Numpad7     NumpadHome    7 / Home key
Numpad8     NumpadUp      8 / Up arrow key
Numpad9     NumpadPgUp    9 / Page Up key
NumpadDot   NumpadDel     Decimal separation / Delete key

Source: List of Keys for AutoHotkey on Windows

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