voltages present on the motherboard

[annalissa]

Hi all,

this is what i have read in the book, "Essential electronics for PC
technicians"

moderns P.C's have voltages present on the motherboard even when the
P.C is turned off

1 to allow faster booting
2 to provide WOL[wake on LAN] and WOM [wake on modem]

Is there any other reason ? which is not mentioned in the book ?

 

[krw]

Hi all,

this is what i have read in the book, "Essential electronics for PC
technicians"

moderns P.C's have voltages present on the motherboard even when the
P.C is turned off

1 to allow faster booting
2 to provide WOL[wake on LAN] and WOM [wake on modem]

Is there any other reason ? which is not mentioned in the book ?

To allow them to power on, in the first place? The (ATX) power
supply uses a "soft" power-on switch connected to the board, which
requires that the supply always deliver power to the board.

 

[Robert Myers]

Hi all,

this is what i have read in the book, "Essential electronics for PC
technicians"

moderns P.C's have voltages present on the motherboard even when the
P.C is turned off

  1  to allow faster booting
  2 to provide WOL[wake on LAN] and WOM [wake on modem]

Is there any other reason ? which is not mentioned in the book ?

It may be a trivial need, but barring use of NTP at boot, a battery
is the only way for your computer to know what time it is.

In the very old days, a PC did not come with a clock and had no need
for on-board voltage when powered off (off was really off). If you
got a clock, you needed a battery.

The addition of a battery allowed the PC-AT to get itself into some
nasty states that required removal of the battery for recovery. If
there is power after shut down, the machine is at greater risk of
storing unwanted or even malicious state. Personally, I'd prefer
boxes that really turned off, even though it is still theoretically
and maybe even practically possible to store malicious state in a
machine with no power in the "power-off" state.

Robert.