The basic gist is this: we started off with AT power, which is “hard power”: when you flip the switch, power is instantly cut to the motherboard. Then, with ATX, “soft power” — software-controlled power — made it possible for the operating system to power off or reboot the system. ATX brought a ton of power management changes, but fundamentally it introduced the concept of standby power, where a 5-volt line to the motherboard is always switched on, even when you’re powered down. This 5V current keeps your BIOS, network adaptors, and other basic components ticking.
Read the whole article here:
http://www.extremetech.com/article2/0,2845,2386668,00.asp
The basic gist is this: we started off with AT power, which is “hard power”: when you flip the switch, power is instantly cut to the motherboard. Then, with ATX, “soft power” — software-controlled power — made it possible for the operating system to power off or reboot the system. ATX brought a ton of power management changes, but fundamentally it introduced the concept of standby power, where a 5-volt line to the motherboard is always switched on, even when you’re powered down. This 5V current keeps your BIOS, network adaptors, and other basic components ticking.
Read the whole article here:
http://www.extremetech.com/article2/0,2845,2386668,00.asp