Re: Aptiva shutdown

Nauzad,

This is an interesting question and one I'd often wondered about myself. Since I didn't know the answer, I asked one of my friends who's a hardware designer for the PC part of IBM's business. Here's what he told me:

The answer to your question is that the power supply in Aptiva can be turned off through a digital interface. There is a digital control signal from the motherboard to the power supply for that purpose. Within the PC BIOS is a program interface that will actually send the command to turn off the power.

The power doesn't really go all the way off, a small amount is supplied to circuitry that requires it so that the system can be restarted if necessary (much like a television set that's turned on and off through the remote control). Aptiva implemented this so it could be used as a telephone answering machine -- you suspend the system (write the RAM onto the hard file) and power off everything except the communication adapter. When the phone rings, the power comes on and the system comes alive from suspension (Wake on Ring). Since everything was stored on the hard file, there is no rebooting of the operating system or invocation of applications required. This allows the Aptiva to respond within a couple of phone rings, rather than a couple of minutes.

A similar feature exists in IBM's commercial PCs, allowing a special command on the Local Area Network ("Magic Packet") to turn the machine on and respond to remote control commands. This is intended for large commercial accounts where the system administrator can install new software, backup data or perform other tasks during the night or weekends when the system is not in use.

It is relatively simple to do this, but does add some additional cost to the power supply, which now has to have a digital control to turn on and off, and has to maintain a low power section all the time.

So, at the boundary between the hardware and the software, the answer is that there's an interface in the Aptiva's BIOS that provides software with the ability to turn the system almost completely off. A BIOS interface is pretty low-level, though, and, for hardware-specific things like this, can be implemented differently (or not at all) on different hardware designs. To regularize how this is done and to raise the level of the interface used by applications, an industry-standard interface to power management has been defined. (Actually, as you will see, the standard covers lots more than turning the power off and on.)

This standard also bears directly on your last question: Can other PCs be shut down through software, too? The answer, is that if they implement a digitally controlled power supply and an interface in their BIOS, they can. And if they implement that in the "standard" way, applications and operating systems can easily make use of the feature. Of course, not all PCs -- particularly older ones -- do this and so they cannot be controlled in this way.

If you need more information on this, please e-mail me and I'll see what I can do.