Date: Wed, 27 Mar 2002 23:49:11 -0800 From: Terry Lambert <tlambert2@mindspring.com> To: "Gary W. Swearingen" <swear@blarg.net> Cc: Seth Hieronymus <sethh@principia.edu>, freebsd-chat@FreeBSD.ORG Subject: Re: processor question Message-ID: <3CA2CAF7.5C661F1D@mindspring.com> References: <OE100msHHbbgCzQ50pF00005549@hotmail.com> <3h663hi3jt.63h@localhost.localdomain>
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"Gary W. Swearingen" wrote: > "Seth Hieronymus" <sethh@principia.edu> writes: > > Do processors use more power / produce more heat when they are doing > > processing other than an idle loop? > > Current-day processors use an extra bit of power every time the state of > one of the millions of gizmos (groups of a few transistors) on the chip > changes. There are a few parts of the chip that are always changing at > a fixed rate (ie, the clock parts) but other parts (floating point and > integer sub-processors, registers, etc) have gizmo-state-changing > happening a lot or a little, depending on what is being computed, and > most (?) processors can be configured to shut down most sections of the > chip into a kind of "hold" state during idle, or not. However, even if all operations in the processor were done in Gray's binary using thermodynamically reversible logic components, the amount of power used by the processor itself is insignificant compared to the amount used by the DRAM (which has to be refereshed when it's not actively being used -- and doesn't have to be when it is actively being used), and all the chips combined pale in comparison to the loss in the stepping transformers in the power supplies, and the magnetic induction motors that run the fans and keep the disk spindles spinning. If you are "lucky" enough to have hardware that is capable of spinning down the drives, bully for you... FreeBSD will spin the things up again because of the syncd, even if there's no real data to write, because not enough state is maintained to let them spin down (it's rare enough when my Windows boxes are idle enough, even when they are idle, to leave the drive spun down for very long; and spinning a drive up takes a lot more energy than keeping it spinning; real equipment (servers) leave the things spinning all the time, and don't try to spin them down). -- Terry To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-chat" in the body of the message
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