Steve Smith talks about ACPI, USB Power, Power states, and why Windows 98 was the first commercially available Windows operating system, capable of turning off the computer itself.
Episode #5-24 released on March 6, 2015
This episode came from a question I got by e-mail. It was related to this person's keyboard still being on, while the computer was powered off. There are many reasons why this occurs, but knowing the origin is almost as important, as knowing why. At least, when it comes to giving you all peace of mind.
Prior to Windows 98, Computers did not turn off by themselves. You would shut down the operating system, and then manually turn off the computer. The bios was primitive, only having hardware settings, some limited plug and play functionality, and keeping track of time.
ACPI, also known as, Advanced Configuration and Power Interface, was released I December of 1996. It was designed to be platform independent, allowing for any properly configured operating system to interact with the bios to enumerate hardware, allow for power management, a varying set of states of power, and included ACPI bytecode in both 16 and 32 bit designs, which would later lead to being able to support more and more ram with time. The 64 bit edition of the ACPI bytecode was released in August of 2000.
When Windows 98 came out, provided the computer it was installed on, had this new ACPI enabled Bios, Windows, was finally able to power off the computer, by itself, instead of forcing the user to turn off the computer after. It, also, introduced the ability to put your computer to sleep (known as S3), and into hibernation (known as S4). However, for this to work, it requires for HID, Human Interface Devices, to remain powered, even if in so-called soft-on, and soft-off modes.
Later on, we got the ability to power on our computers by our keyboards, even when on soft-off (known as S5), we are able to use the RTC alarm to wake up the computer based on time, wake via the modem, and even now, wake on LAN. This means that the bios now exhibits many more states that just being on or off. We have many different levels of power now. As part of my show notes, I have indicated that value next to the state already. Now, a computer in S5 state, is known to be off by most users, however, there is still power to the power supply, and the mainboard, allowing the bios to respond to a S0, which reboots the computer, empties the all the caches, and no previous content or commands is retained from the previous session.
Even while in S0, your computer, is technically on. Newer mainboards, and some cases power supplies, have the ability to have all, or a selected few, ports, normally USB ports, powered. There is even the ability to power and recharge other devices while in this state. Many newer wireless mice charge because of this fact. You can charge cellphones, and tablets, as well. This is why your computer's keyboard is still, powered on, even while it is off, because it is not actually off.
To do any hardware changes, computers are required to be in a G3 state, known as mechanical off, which is only achievable by physically turning off the power supply unit, and in some cases, unplugging the power cable.
Now, some of you may be wondering if there is a way of turning off completely the computer, when the operating system is off, and the answer is no. You have to unplug the computer. In the case of laptops, you must, also, remove the battery.
You can, however, disable, various modes in the bios, provided the bios allows you. If you are worried about people being able to access your computer remotely, you have to turn off modes like wake on LAN, and wake on modem. You may choose to turn off all the wake from settings in the bios, to be absolutely sure. Your computer will still be in soft off mode, but your computer will not power unless the power switch is explicitly engaged. If USB power is not required, and causes you some concern, you may, also, in some bios versions, turn off power to USB ports while powered off, however, you might have to search for the instructions for your mainboard.
So, for all others, the reason why your keyboard, mouse, cellphone, tablet, etc... is still powered, even while your computer is off, is by design. Thanks to the advent of ACPI in December of 1996, we can have the operating system turn off the computer, put our computer to sleep, have it hibernate, and now, even charge all our devices.
For those interested, the entirety of the ACPI Project was transferred over to the UEFI Bios Project, and the latest revision for ACPI, Revision 5.1, was released on my birthday, August 12, 2014.
Have a great day, I hope this answers your questions, and concerns.
Host : Steve Smith | Music : Jonny Lee Hart | Editor : Steve Smith | Producer : Zed Axis Productions