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Tripping On Power: Page 8 of 14

Because of the number of reduced power states and clock rates and the ability to quickly change states, power consumption can be regulated almost down to the instruction level. So while SpeedStep may have been analogous to turning off cylinders in an engine, Foxton is more like a gas pedal, allowing for more rapid performance changes. The result is the impressive power savings announced for the dual-core Itanium. Intel says the dual-core Xeon chips bound for servers will also get Foxton technology.

Not to be outdone, AMD has adapted its laptop PowerNow! technology for use on the Opteron. Dubbed PowerNow! with Optimized Power Management (OPM), the technology allows for independent control of voltage and clock frequency, each in 32 increments. PowerNow! with OPM should perform similarly to Foxton.

Both power management technologies operate partly independently and partly with the involvement of the OS. This support is just coming out now. In the future, Intel and AMD are likely to follow a course pioneered by IBM. This calls for shutting off various parts of the CPU when not in use. For example, if they're not needed, banks of cache memory or floating point units can be turned off. As the multicore strategy plays out, entire cores can be shut down when not needed.

COOL DRIVES

Drive makers are also getting into the act by offering a variety of power-saving states on their devices. In order to save power, drive makers have a number of options at their disposal. Hitachi, for example, offers three lower-power states for its Serial ATA (SATA) drives. These include simply sending the heads to their rest position, or either slowing down or stopping the drive mechanism altogether. The table above shows the four drive states offered on SATA drives, along with the resultant power savings and recovery times. Originally intended for Energy Star-compliant desktop computers, these modes can also be useful in some data center applications. Typically, power-saving modes aren't available on Fibre Channel or Serial-Attached SCSI (SAS) drives. These drives are intended to run constantly, whereas SATA drives were designed to be frequently powered on and off.