Posted on 2005-04-28
Last Modified: 2010-04-26
just a curious questions

you know how on those old computers when you turn off your computer by going to start shutdown and all and it turns off but not all the way. It will say " It's now safe to turn off your computer" why does it say that . Why can't it shutdown.

My theory is something to do with the power supply.


Question by:theitguy
    LVL 33

    Expert Comment

    The message is to indicate that the system has closed open programs( which u might not 've during shut down )
     and saved settings to your hard disk.
    LVL 33

    Expert Comment

    Nowadays most computers are built with Advanced Power Management Systems which can automatically turn themselves off following the shut down command from within Windows
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    Accepted Solution

    >> My theory .... the power supply <<   Correct. AT powersupplys can not turn themselves off. That came with ATX powersupplys. Started with the Socket7 (Super7 ?) mobo's <Pentium I>. Some of them had both the 2 inline connectors (AT), and the 20 pin double row connectors (ATX).
    LVL 26

    Expert Comment

    Yes yes yes..

    ~ Sort of...

    The old AT power supplies were 'dumb' power supplies.
    You turn them on, they send out power.
    You turn them off, no more power.

    The problem was if you shut off the thing when the system was still doing something you could lose data (or even damage a hard drive due to a sudden power loss) so they invented that "It's now safe to turn off your computer" funtion which is basically the system telling you it has completed everything, the drives are done, and it's okay to cut power.

    The newer ATX power supplies unless UNPLUGGED from the wall or turned off via a manual switch (which only some have) on the actual power supply ARE NEVER completely 'off'. They send a small voltage to the motherboard 24/7/365 if they are plugged in and that switch (if present) is on. This voltage is used more or less as a remote control to turn on and off the main part of the power supply to power up or down the rest of the system. Newer operating systems won't let the signal to shut down go until they are done anyway so there in no need for the "It's now safe........." screen.
    [ Many systems allow disabling the auto shutdown through the BIOS. Most people don't set them up that way but if they did the "It's now safe....... " screen would come back and you would again have to use the switch to turn it off.]

    Expert Comment

    Good answer PCBONEZ...

    You can also use the Wake-Up features of an ATX (ACPI) PC. For example a Wake-On-Lan feature, which turns the PC on if the network card
    detects network activity.
    LVL 33

    Expert Comment

    : )
    LVL 33

    Expert Comment

    Thank you much.    : )

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