How does Restart differ from Shut Down+Boot?

Doctor Q

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Sep 19, 2002
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My friend just showed me that if his iMac loses its connection to his wi-fi network, restarting the iMac doesn't help, but if he shuts down the iMac and immediately boots it back up, it connects to his wi-fi network without any trouble. It's happened more than once, so he uses this trick whenever he needs it.

What's the reason? How does restarting differ from shutting down and booting?
 

Significant1

macrumors 6502a
Dec 20, 2014
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A restart doesn't cut the power, so if a chip as entered a non-working non-default state which is not initialized during boot, it will keep that state.
 
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MacDawg

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Mar 20, 2004
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I have several Windows 7 touch screen terminals that I manage for work
On 2 occasions, I have had touch screens become unresponsive

A restart would not fix it
and a shut down did not fix it
BUT a shut down and the power cord disconnected would (found the trick on the interwebs somewhere)

I found that interesting
 

Doctor Q

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Sep 19, 2002
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Los Angeles
A restart doesn't cut the power, so if a chip as entered a non-working non-default state which is not initialized during boot, it will keep that state.
Could the chip's "stuck state" be due to either a hardware or software cause?
 

chown33

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Aug 9, 2009
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Could the chip's "stuck state" be due to either a hardware or software cause?
Yes. It could be either one alone, or perhaps even a combination of both.

There may also be other things that contribute, such as thermal effects. For example, if a chip works fine when it's cold (room temperature), but it then starts misbehaving when it gets warmer. After reaching that thermal threshold, it then takes a power-cycle (down then up) to get it to start behaving again, at least for a while.
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I have several Windows 7 touch screen terminals that I manage for work
On 2 occasions, I have had touch screens become unresponsive

A restart would not fix it
and a shut down did not fix it
BUT a shut down and the power cord disconnected would (found the trick on the interwebs somewhere)

I found that interesting
There's a "trickle power" voltage coming from most power supplies these days. It only turns off when the mains power is removed. Turning off the power switch doesn't remove trickle power.

Sometimes this symptom means that a battery in the computer is too low, and the non-volatile parameter storage is getting corrupted. Replacing the battery may solve the problem. Not always, but it's worth looking at.

Those aren't the only possibilities, but without knowing what the actual electronic circuitry is, it's a fair guess.
 
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