DeWhitt cites two reasons for optimizing idle power consumption on the machine. First, he points out that a PC is idle various times throughout the day, and the more the system gets to that state and remains idle, the less power it uses.
Second, he notes, "idle power consumption is the 'base' power consumption of all other workloads." When the machine has other workloads, it will consume additional power over that idle power. Lowering that idle power consumption leads to improved energy efficiency. Achieving that goal, per DeWhitt, entails optimizing the amount of processor, memory, and disk utilization.
The Windows 7 team reports areas of investment in the OS that help reduce process utilization, thereby enabling longer periods of time where the processor can enter into low-power modes. " One of these investments is in the area of services that are running on the platform and having those services only start when they are required, referred to as 'Trigger-Start,'" writes DeWhitt. "While these services are efficient and have minimal impact by themselves, the additive effect of several services can add up. We are looking at smart ways to manage these services within Windows but also making our investments in this area extensible for others who are writing services to take advantage of this infrastructure."
The Windows 7 team is also focusing on improving core-processor power management: The OS "scales processor performance based on the current amount of utilization," DeWhitt writes, "and making sure Windows only increases processor performance when absolutely required can have a big impact on power consumption."
USB devices and their impact on energy consumption has not been forgotten. The team has injected in Windows 7 the ability to selectively suspend USB devices of all types, including audio, biometrics, scanners, and smart cards. That translates to a more energy-efficient PC, according to DeWhitt. Beyond USB devices, Microsoft has improved power management of both wired and wireless networking devices.
Road warriors who watch movies in transit will be happy to know that with Windows 7 comes the optimization of DVD playback, including reduced processor and graphics utilization, audio improvements, and optical disk drive enhancement. The payoff: increased battery life across a broad range of mobile platforms, according to DeWhitt.
In its quest to reduce energy waste, the Windows 7 team also honed in on extensions, including graphics devices, device drivers, background services, and installed applications. "Large improvements in power consumption and energy efficiency can be realized by improving the efficiency of platform extensions," writes DeWhitt.