What is ACPI?

We all like to put our PC into hibernation instead of always shutting it down right away. But how does this work? ACPI makes it possible. Let’s take a closer look at this standard.

ACPI is the abbreviation of "Advanced Configuration and Power Interface" and describes an open industry standard for power management of PCs, laptops and servers. In order to use ACPI, an ACPI compatible hardware (motherboard, power supply etc.) and an ACPI compatible operating system (for example Windows) are both required. ACPI was released in 1996 and is being developed by Intel, Microsoft, HP and other IT-companies. The control over the power management lies in the operating system. It has a better overview of the power requirements of the computer and the possibilities to save energy than the BIOS. In contrast to its predecessor APM, with ACPI the BIOS only has the task to communicate with the hardware.

What is APM?

APM stands for "Advanced Power Management". The term also describes a standard for energy-saving methods for PCs. APM was developed by Intel and Microsoft in the early 1990s. The power management features of this standard are mostly managed by the BIOS and hardware. However, since the appearance of ACPI, APM has played only a minor role.

How does ACPI work?

To better understand how ACPI handles power management, we need to go further and look at the different states in which a computer with ACPI can be. The so-called G-state describes four possible states: the mode "G0" designates the active state ("Working"), in which one can work, "G1" the sleep state, "G2" is the so-called "soft-off", a PC with ATX standby voltage, while "G3" describes the unplugged computer ("Mechanical off"). In the case of the "G1" state, you can now distinguish between the various sleep states (s-states):

  • S0: Working – The system is switched on, functional and fully operational.
  • S1: Sleep – Simple sleep mode in which the CPU is stopped.
  • S2: Deeper Sleep – Extended sleep mode, where other components such as the cache of the CPU are turned off.
  • S3: Standby Mode – Much of the motherboard’s hardware is turned off. This mode is also referred to as "Suspend to RAM" (STR) or "Suspend to Memory" (STM), that is, the operating state is still stored on a volatile memory (RAM).
  • S4: Hibernation – Also "Suspend to disk" (STD) – that is, the operating state is backed up to non-volatile memory (hard disk or SSD). The system can be disconnected from the power.
  • S5: Soft-Off Mode – System is switched off (shut down), only the power supply provides power. The system can be activated via a power button or optionally via Wake on LAN.

In addition to the G and S-states, a further distinction is made between ten different CPU states (short "C-states") and five possible device states (short "d-states".

What are the Advantages of ACPI?

The advantage of standby and hibernation is, that the PC does not have to reboot completely and is ready for use more quickly. During these modes, we can also keep programs and files we are working with, open.

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4 Jun 2019 Array ( [id] => 423 [title] => What is a power button? [authorId] => [active] => 1 [shortDescription] => Since we already talked about ACPI and the different states of energy a PC can be in, we continue our little series with the power button. How does it work and what alternatives are there? [description] =>

The power button is, as the name implies, a switch that can be used to switch electrical appliances on and off. In computers, such as our Mini-PCs, the functionality is now limited to switching on. Whereas in the past, at Windows 95 and such, we had to wait a few minutes until the PC shut down and could be switched off, this now happens automatically. Only for hard reset during operation – for example if the PC hangs – it is still needed. Since this can cause software problems, we should only do this in an emergency. Depending on the settings in the software, the Power Button can also be used to put the running PC into hibernation.

What does a power button look like?

Unlike the interfaces, for instance, the appearance of the power button is not specified. It can take various sizes and shapes, depending on how it fits the design or is practical. Often, the power button has an integrated LED that lights up to signal that the PC is running.

How does a power button work technically?

The power button has a cable, which is connected to two pins on the motherboard. By pressing the power button, a circuit is closed on the mainboard. At that moment, the power supply receives the signal to supply the computer with power and thus start up.

What advantages does the power button have?

Actually, the power button is a very practical invention. After all, it offers the great advantage that we can easily turn a PC on, and in emergency also off.

What are the disadvantages of the power button?

The disadvantage of the power button is that we always have to be close to the PC if we want to turn it on. In many industrial applications, however, the computer is permanently installed and is not necessarily freely accessible. Luckily, there are other ways to turn on a PC.

What are alternatives to the Power Button?

One alternative is an external power switch, as it is offered for example for our BOX N2930. Using a cable, the power button can be placed outside, while the PC is installed in a cabinet, stele or the like.

Another option is Wake on LAN, which starts the PC via the network card. In addition, a computer can also be started via the keyboard or mouse and thus via USB (Wake on USB). The only requirement for these possibilities is ACPI.

Another example is the ultra-small single-board computer Raspberry Pi. It does not have a power button, Wake on LAN or anything like that (because it does not have a BIOS) but boots, when it is supplied with power. To turn it off, like all the other PCs, it has to be shut down manually.

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know-how
What is a power button?
Since we already talked about ACPI and the different states of energy a PC can be in, we continue our little series with the power button. How does it work and what alternatives are there?
11 Jun 2019 Array ( [id] => 427 [title] => What is Wake on LAN? [authorId] => [active] => 1 [shortDescription] => Here comes the last part of our small series about switching on and off a (Mini) PC. After talking about ACPI and the Power Button we now take a closer look at Wake on LAN. [description] =>

As the name suggests, "Wake on LAN" (short: WOL) describes a standard to start a PC via the built-in network card. This can be done on the one hand via the local network, on the other hand, WOL offers the opportunity – and here comes the great advantage – to turn on the computer via Internet.

 

What are the requirements for Wake on LAN?

 

A prerequisite for Wake on LAN is that both, the motherboard and the network card, support the WOL standard. In addition, ACPI or at least its predecessor APM must be activated in the BIOS and the PC should run a current version of Windows, Linux or Mac OS. With Wake on LAN, a computer can be awakened from the idle states S3 (Standby/STR), S4 (Hibernation/STD) and S5 (Soft-Off). (In our article on ACPI we have explained the different states in more detail.) However, it is important that the network card is permanently supplied with power via a standby branch of the power supply – even if the PC is switched off. In addition, the computer must be connected to the router via a network cable.

 

How does switching on via Wake on LAN work?

Switching on is done via a so-called "Magic Packet", that is sent to the network card. It contains the hexadecimal value FF six times in succession, followed by the MAC address of the network card, which is repeated sixteen times without pause. This Magic Packet can be sent from another computer on the network. If you are not on site and would like to switch on a PC via Internet, you can use a different PC, a smartphone or even a NAS. Detailed instructions on how to configure a computer for Wake on LAN can be found here.

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know-how
What is Wake on LAN?
Here comes the last part of our small series about switching on and off a (Mini) PC. After talking about ACPI and the Power Button we now take a closer look at Wake on LAN.
26 Jun 2019 Array ( [id] => 429 [title] => What is iAMT? [authorId] => [active] => 1 [shortDescription] => If you look more closely at Intel Core i processors, you may come across the term "iAMT", short for Intel Active Management Technology. In this article we have summarized , what stands behind it and what functions iAMT has. [description] =>

Intel Active Management Technology, iAMT  for short, is a system for the administration and remote maintenance of PCs. It is based on the Intel vPro platform and consists of its own hardware component, the Intel Management Engine (Intel ME for short). It is installed as a microcontroller in all current chipsets, including Intel Core i3, i5, i7 and Xeon processors.

This microcontroller always runs when the computer has power, since it is supplied with power via the 5-volt supply of the power supply. The PC does not have to be switched on for this. This hardware-based management has the advantage that most features can also be used when the PC is turned off or crashed. There are only a few functions, the PC needs to run for. The computer, which is to be managed via iAMT, can be controlled via cable or WLAN.

What functions does iAMT have?

iAMT can perform various tasks, e.g.

  • Turn the PC on or off remotely
  • Steer the boot process in a different direction, e.g. to boot from a CD
  • Reset the computer
  • Change BIOS settings
  • Turn power supply on and off
  • Redirect keyboard, mouse and display output via the KVM switch
  • Get information about errors
  • Initiate remote control sessions

What are the disadvantages of iAMT?

Unfortunately, iAMT has enormous security holes. The German Federal Office for Information Security already warned in 2015 about the Intel Active Management Technology. In 2017 it became known that is was possible to take over computers completely. More information can for example be found here

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know-how
What is iAMT?
If you look more closely at Intel Core i processors, you may come across the term "iAMT", short for Intel Active Management Technology. In this article we have summarized , what stands behind it and what functions iAMT has.