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Chapter 2: Power Management History and MotivationIn the early days of pers nal computing, under the DOS and CP/M operating systems, there was no power management —computers either used 100 percent of their power requirements or were switched off. Personal computer power management history dates back at least to1989, when Intel shipped processors with technology to allow the CPU to slow down, suspend, or shut down part or all of the system platform, or even the CPU itself, to preserve and extend battery life. The increasing importance of power management reflects the increasing number of PCs in use and their transition to tools that go wherever people go.
Three interlocked tracks guided the development of PC power management —one for power management specifications, one for system design specifications, and one for application specifications. Figure 2. 1 shows the timeline for key power management and system design specifications;application program power management specifications are defined by the underlying ACPI operating system.You'll learn later in this chapter how problems in early power management technology, particularly the Advanced Power Management (APM) Specification, directly influenced the design of the Peripheral Component Interconnect (PCI) and ACPI specifications.
Responding to RequirementsMobile computers started the drive for PC power management. Early attempts, including the Osborne computer and "luggable " PCs with cathode ray tubes, drew so much power they had no alternative but to plug into external power sources. The development of low cost, reliable liquid crystal displays (LCDs)made battery powered laptops possible in the late 1980s, and once hardware technology crossed that line, a sequence of hardware and software improvements began that have combined to increase the performance and on-battery lifetime of laptops.
The monumental number of PCs operating worldwide creates other requirements for PC power management. Because there are hundreds of millions of PCs in operation, the installed base of computers worldwide consumes tens of gigawatts for every hour of operation. Even small changes in average desktop computer power consumption can, on the global scale, save as much power as generated by a small power plant.
Mobile and Battery Powered ComputersTable 2.1 shows the historical mobile platform power road map, detailing the ever-increasing power required for increased performance in all subsystems. Mobile computers use the least power of any PC platform, both to extend battery life and reduce heat dissipation. However, the increasing power demands from the constant drive to increase mobile computing performance to near-desktop levels mean even these limits will go down over time.
Energy Star GuidelinesThe United States Environmental Protection Agency (EPA)publishes Energy Star guidelines that suggest ways to reduce power consumption. Addressing the power consumed by the many computers in use, the EPA notes:
A typical computer, monitor, printer, fax machine, and medium speed copier cost about $185 annually to operate, not including the cost of paper. Operating similar equipment that meets the Energy Star criteria costs about $97. Turning off the equipment at night can cut the annual energy costs even further.
The Energy Star label identifies energy efficient products that save money by eliminating unnecessary energy use. Energy-efficient office equipment saves energy by powering down and going to sleep during periods of inactivity, but retains all the performance features of standard equipment. On a monthly or annual basis, this equipment uses about half as much energy as standard equipment, saving owners millions of dollars in electricity costs.
The EPA is interested in power management for another important reason:using power management in office equipment offers huge potential for dramatically cutting air pollution associated with electricity use.
The Energy Star guidelines also have been adopted outside the United States. Although power c sts overall have declined in the U.S., they have increased in other parts f the world. Increased power costs underscore the benefits of using Energy Star qualified products.
The Energy Star guidelines introduced in 1993 required computers to consume less than 30 watts when in their reduced-power state. Revised guidelines effective as of January 1, 1998 imposed the requirements in Table 2. 2, making it possible for workstations to qualify for Energy Star compliance.
A clarification to the standard published in April 2000 notes that the operating system is typically a key component for entering and recovering from sleep modes, and requires that all necessary software to enable sleep modes be provided by manufacturers. The Energy Star web site (http://www.energystar.gov) provides the latest updated specifications.
The Energy Star guidelines for computers require sleep state power consumption of 15 watts or less. In addition, computers must be able to maintain communication and wake up on demand.