12.3.1 Portable Power

Learn the concepts behind portable power management for laptops.

Laptops are designed to be portable and run on battery power for extended periods of time. In order to not consume power like a desktop does, laptops:

• use specially designed low-power components
• utilize a power management process that's much more efficient than what desktops use.

Advanced Power Management (APM)

Laptops used to use a tool called APM. It's rarely used today but still can be found in legacy systems.

Advanced Configuration & Power Interface (ACPI)

Many portable devices use some form of ACPI to prolong and optimize battery usage. With ACPI, hardware configuration settings are only controlled by the OS, known as OS-directed config and power management (OSPM). Using OSPM, the OS receives real-time stats on how much power each component is using. The OS can use this to dynamically change the amount of power each component is receiving, from increasing, decreasing, or powering it off.

ACPI Power States

Working

In this state, the entire system is usable, and hardware that isn't being used can enter a low-power state to a high-power state very quickly so it can respond to hardware or network events.

Sleep/Standby

Depending on the OS, sleep and standby are the same thing e.g. macOS. In this state if the system's battery charge falls below a preset threshold, the system will hibernate. In the hibernation state RAM is saved into a file for preservation, and the system powers down. The system will power on from a keyboard, mouse, or display event e.g. lid up.

Off

Guess what this one does.

Fast Startup

Windows is another option that's enabled by default. It changes the way the system powers down. Normally, all the running programs are terminated and the user is logged off before the machine powers off. However, with fast startup enabled, the user is logged off but all the files and programs are hibernated. When the system is restarted, the state is restored to where the user left off, called a hybrid shutdown.

USB Selective Suspend

This feature kills power being sent to USB ports that aren't being used. If the port is being used, but no data is being sent/received, power can still be killed.

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