– how does a computer prevent itself from fully shutting down when you restart it?
In: Engineering
Depends on the operating system and computer architecture that you use. First of all, it may be helpful to clear out the idea that restarting is somehow “less of a shutdown” than actual shutoff is.
* Per default Windows settings, a restart actually closes all processes, whereas a shutdown keeps Window Kernal (all windows operations and routines) saved and stored on a file, so than next time you turn on the computer, it simply loads from this stored file.
* A restart on the other hand actually shuts down the kernel and everything and clears it out.
* It is for this reason that whenever you do a software update, Windows directs you to restart rather than shut down.
* This is the default setting. To get rid of it, you need to disable “fast startup” in the windows settings. In my personal opinion this should never be be the default setting in the first place, because it is counterintuitive.
Now that this assumption has been cleared, to answer your question the actual “restart” and “shutdown” and “power on” are all a very complex steps of routines and processes. Both restart and shutting down does a whole bunch of steps like closing programs, disconnecting network, etc. Where they diverge is that eventually shutdown disconnects power from the motherboard, while restart never disconnected the motherboard at all.
It is for this reason that when something is broken, you get the classic “have you tried unplugging it and plugging it back in again?”. As an Electrical Engineer myself, I personally prefer a physical switch, instead of these small signal processes that are used to turn on the computer nowadays.
The restarting process is just telling the PC to reset itself, that’s why. Nothing special going on, just a STOP and GOTO 1 command essentially. The power never cuts. The OS just reruns from the 1st line.
During every start, power gets applied, then the reset signal is triggered so the chips start working from a defined initial state.
A reset does not cut power, but it triggers the reset signal so everything start from initial state again.
What do you mean by “not fully shutting down”?
a computer never fully shuts down, even if it is unplugged, there is a tinny battery in it keeping some of the systems alive (mainly the clock). There are other systems that are always on if the computer is plugged in. One of these is told “Hey, we are shutting down, once we do, turn the computer back on.” So it does. This subsystem can also handle turning on the computer at a specific time (for updates at midnight say)
It wasn’t that long ago that computers weren’t able to control the power themselves. I remember shutting down Windows 95 and it showed a message saying “you can now turn off the your computer”.
ACPI is a communication method between the power supply and the CPU (and other parts of the system), to control when the power is applied and the various sleep states that system supports, up to and including power off. The CPU controls some of that, but generally the power button (quick press to reset and 4 second press to really really turn off) is nothing to do with the CPU and everything to do with the PSU.
Your computer is some half a dozen computers in a trenchcoat. One of them (the ACPI system) manages the power state of the rest and never shuts off. When you restart the PC, it gets a request to cut and restore power to the other stuff for a moment.
Things start things, for example, you turn the key In a car and the electrics come on, turn it further and there’s ignition and the engine starts. These are the “initialization” steps, for computers normally restarting is only related to the software and processes, so you could kill the software and OS, but all the heart(motherboard) and brains(memory/storage) are simply not being used but are still be supplied power. Restarting software is very simple and doesn’t have to restart hardware.
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