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Noticed this keyboard that has a "Wake Up" key next to the "Sleep" key.

enter image description here

What is the use of this key?
Most keyboards I know that have a Sleep key don't have a Wake Up key; to raise a computer from sleep mode you can press any key.
So, does this key actually have a function? Are there systems (or have there been systems in the past) that can be woken up from sleep mode only with this key?

I did search the net, but other than comments about some keyboards having this key and others not, I didn't really find any indication that it was really needed in some circumstances.

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  • Steve Jobs would have disgorged it - laydros.freeshell.org/docs/stevekeys.html – Adit Gupta Aug 18 '15 at 14:44
  • It is scancode E0 63 but I guess that your computer still first have to listen for the keyboard for it to have any effect. Generally your computer already needs to be out of sleep to do that, or any action of the USB keyboard already does this. So the only thing I can think of is a special chip that does this while listening to PS/2 signals. I can simulate the key on my Ultimate Hacking Keyboard, but it of course doesn't do squat. – Maarten Bodewes Oct 23 '18 at 3:44
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There were several versions of BIOS (Basic Input Output Systems) that came on motherboards in the 1990s and 2000s that had an option to choose when to resume. These systems usually had an entry named "Resume From S3", and allowed you to select from several options, such as "any key," "power key," or "wake key." However, in all cases, there were other optional means of resuming, usually by hitting the power button or even a sleep/wake button built into the case that was directly wired to the motherboard. The wake button is largely obsolete (I don't think I've seen one in the past decade).

The S levels are defined by ACPI, where each increase in S level results in further power savings at the expense of how long it takes to resume normal operations. S0 simply turns off the monitor(s)/video cards, S1 turns of non-critical devices and suspends CPU usage, S2 flushes CPU buffers for additional power savings, S3 powers off the CPU entirely (but the RAM retains power), S4 is the so-called hibernate level (suspend to disk), and S5 is "fully shut down" (full reboot required to start up again).

Devices with S4 resume options can be resumed even while hibernate is active. Without S4 resume options, the only way to wake a system in hibernate is by pressing the power button, but other options can monitor the system inputs (e.g. USB keyboard, PS/2 keyboard) for a valid wake signal, such as the Wake key.

enter image description here

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  • OK. I'm not entirely sure what your screenshot is saying with S3 and S4, but I'll take your word for it! My computer's BIOS has "USB wake up" that you can enable or disable, but no "keyboard wake up". – Mr Lister Aug 19 '15 at 8:51
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    @MrLister See ACPI, but basically S3 is a sleep mode where only RAM remains powered on (CPU and most devices are powered off), and S4 is a state where RAM is stored to disk and then powered off ("hibernate"). Each increase in "S-Level" results in further power savings at the cost of more expensive restore times (it takes less time to get from S3 to active than it does S4 to active). – phyrfox Aug 19 '15 at 13:14
  • Ah, OK. Thanks! You should add that to the answer, by the way; it might get lost as a comment. – Mr Lister Aug 19 '15 at 14:30
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I think it's one of those things where you provide an obvious button that everyone could find to wake-up their computer. However, as you mention and probably most people now know is that you can in fact use different triggers to wake up your computer. Perhaps this was added because somebody assumed that this would be the what novice users would do, but than the actual implementation accomodated for the user instead.

Don't get me wrong, there are people who use and probably set up their computer to only listen to that event, I think, however, that in most use-cases the now common and current approach is just as good; which is wake with whatever comes naturally - be it the power button, the keyboard, ...

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  • What I'm most curious about is, have there been systems that could only be woken up with the WakeUp key? Or was the implementation always "all keys can wake the system up" from the beginning? – Mr Lister Aug 18 '15 at 13:26
  • There was a time where you'd actually have to set up the triggers from which a computer would have to wake, like keys, WoL, Timers and so on, in fact there are still systems that have this as a default. In a time not so long ago, you'd to connect the Wake-on-LAN interrupt from your network card to your main board... – Xabre Aug 18 '15 at 13:28
  • I think I misunderstood your question a little bit; short answer no, there was (fairly sure) no time in which this was the only way to really wake your computer; it serves more as a helping hand ;-) – Xabre Aug 18 '15 at 13:39
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    Less likely for the cat to interfere, seems like a nice option to me. The cat can sleep on the keyboard without waking up the computer either. – user67695 Sep 14 '17 at 13:55

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