Introduction

Computer performance have increased at an amazing rate in recent years, and unfortunately so does power consumption. An ultimate gaming system equipped with a quad-core processor, two NVIDIA GeForce 8800 Ultra, 4 sticks of DDR2 memory and a few hard drives can easily consume 200W without doing anything! To reduce power wastage, a few industry standards have been developed to make our computers work more efficiently.

In January 1992, Intel and Microsoft developed APM (Advanced Power Management) to manage power when a computer system is idling. Later in December 1996, the successor of APM – the Advanced Configuration and Power Interface (ACPI) specification was developed by Compaq, Microsoft, Intel, Phoenix and Toshiba as the industry open-standard power management interface. What's the difference? Let's take a look :

Advanced Power Management (APM) Advanced Configuration and Power Interface (ACPI) • Cheap implementation, but not effective.

• Application and driver send control to APM driver directly.

• Device power is managed by its own driver.

• Other hardware like CPU is managed by APM BIOS.

• Power management state machine is done by APM BIOS since it is simple. • Implementation is more costly, but effective.

• Application doesn't need to manage power.

• Device driver uses ACPI to interface with hardware power management.

• ACPI is abstract, thus OS and hardware can evolve separately.

• Power management state machine is complex, hence handle by the operating system.

In this article, I will not go into APM as most PC use ACPI these days.