Actions from either outside of the PC (e.g., the keyboard, mouse, network or modem connection), or internal sources (computations, internal timers). The occurrence, or lack of occurrence, of different kinds of activities are used to determine when the PC should enter and leave low-power modes.
APM is a standard that defines mechanisms by which
the CPU controls power use by various system components while
the system is in active use (see Intel/Microsoft, 1993 for further
details).
The BIOS is the interface among the processor, cache and main memory and system busses which lead to add-on cards and some external peripherals, and also controls the initial stages of system start-up. The BIOS is a key element in most implementations of power management.
A Cathode Ray Tube is the standard "television"-like screen found on most PCs.
The doze mode is the first level of processor power management. The system clock slows or even halts.
DPMS defines four power management modes for monitors: On, Stand-by, Suspend and off. The presence or absence of particular (horizontal and vertical) synchronization signals or the entire video signal indicate to the monitor which power management mode to enter.
The ENERGY STAR program was created by the U.S. Environmental Protection Agency to encourage the manufacture and use of office and other equipment that reduces energy use and hence pollution from power plants. Section 1.3 and Appendix B describe it in more detail.
A mode in which the CPU is fully active, and either computing or capable of doing so with no delay. The hard disk may be powered down with the processor in full-on mode.
Integrated Drive Electronics (IDE) drives are used on nearly all Intel-based PCs for the internal hard disk. Secondary disks may be IDE or SCSI. Both schemes define how information and control is communicated between the processor and disk.
An interrupt request is the method that one part of the PC uses to signal the processor that some event of possible interest has occurred and might require action. IRQs relevant to power management include the mouse, keyboard, and network interface, as they may indicate that the machine should emerge from a low-power mode.
A Liquid Crystal Display (LCD) screen is used on most laptop computers. LCDs use much less energy than a CRT
The monitor for a PC is usually a cathode ray tube (CRT), and serves to display visual information.
The Swedish organization NUTEK publishes a specification for monitor power management.
In this guide we generally use "PC" to refer to the processor and related hardware (that is, excluding external disks, printers, etc.), and not including the monitor. Sometimes "PC" refers to the entire system, but it should be clear from the context when this is meant. "Computer" power management includes PCs and monitors, as well as workstations.
Instantaneous electricity use (power) is measured in watts (W), with the amount of electricity used over time typically measured in kilowatt-hours (kWh).
Power management uses firmware, hardware and software solutions to conserves energy when the computer sets idle and enters defined states of inactivity.
The Small Computer Serial Interface protocol defines how a processor and many device types can communicate, including, but not limited to, hard disks. The most common other protocol is IDE.
Sleep and Standby are the first low-power stages that turn down or turn off some peripherals and allows for almost immediate recovery.
The lowest powered mode for a PC. As many system components as possible are powered down, and the processor is halted.
A Universal monitor will begin power management from either DPMS signals or a completely blank screen (typically generated by a properly configured screensaver program) and so can be used on a PC not designed for power management.
A microprocessor in the family 286, 386, 486, and Pentium®, usually made by Intel, but also by other manufacturers.
Continue to Chapter B:
Resources.
Return to the PC User Guide table of contents and home page.
Return to Appendix 8: References.