Spin down harddrives. Worth it?

Are people still spinning down their harddrives?

I tried setting the harddrive in my laptop to spin down after 1 minute of inactivity, and noticed that the battery life has not lengthened significantly (didn't time it). I'm sure the drive was spun down, as I can hear the motor when it's running. When an application needs to access the harddrive when it's spun down, there's about a 3 seconds delay. Definitely noticeable. It needs to wake up once every few minutes, too, to commit the journal to disk.

I looked up the specs of my drive -
WD Scorpio Blue 320 GB SATA Hard Drives ( WD3200BEVT )

and it says -

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Power Dissipation
Read/Write 2.50 Watts
Idle 0.85 Watts
Standby 0.25 Watts
Sleep 0.10 Watts

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(By the way, what's the difference between 5V DC and "power dissipation"? I have always thought P=IV, and it only doesn't agree for the "Idle" power)
I'm assuming idle means still spinning, and standby means spun down.

For 0.5W difference... I don't know. And then motors draw high currents spinning up, so there may be no power saving at all if spun up frequently enough! (just free lag)

I was surprised that by default, Ubuntu doesn't spin down laptop harddrives on idle. I'm beginning to see why.

Is there a way to use a USB Flash Drive on Linux the same as the ReadyBoost feature of Vista?

Edit: Oops, didn't even see your other post about ReadyBoost for Linux before replying. :)

Yeah, P = UI (or P = VI for you US junkies, shame on you).
I tend to not spin down the drives. It saves an insignificant amount of power for it to be worth it. It's annoying when it has to spin up again.

I don't know why you think it doesn't seem to agree?
If U = 5V, and it uses 2.5W, then it means it uses 0.5A. Or does it say differently somewhere?

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Originally Posted by Elysia

Yeah, P = UI (or P = VI for you US junkies, shame on you).
I tend to not spin down the drives. It saves an insignificant amount of power for it to be worth it. It's annoying when it has to spin up again.

I don't know why you think it doesn't seem to agree?
If U = 5V, and it uses 2.5W, then it means it uses 0.5A. Or does it say differently somewhere?

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Interesting
What does U stand for?

In Canada, I learned it as: P = EI

E = Electromotive Potential

U stands for voltage. The standard letter (except for USA who uses V).
I suspect you are talking about the voltage you get from a battery whose term I cannot name in english. It is not different from U except the the voltage from a battery will drop as the load increases.
But, generally, in your normal formula collection, it is named as P = UI. A battery is often seen as a voltage source and a resistor connected serially.
Well, doesn't matter much in this case since the voltage should be constant.

Is your power bill high or something? Spinning down your drives is insignificant in savings but far more significant when a program needs to use the drive. It can cause serious lag in games for sure and sometimes if the data is time critical it can cause apps to crash if they do not handle the situation correctly.

Bubba: Most of these discussions for things like spin downs are about laptops and typically not about desktops. (Though for home server usages there is talk of power concerns due to 100% desired uptime)

It is still a moot point.

Yeah, it's about laptops. I heard it's really bad for desktops, since desktop drives are designed to take a lot less load cycles (or whatever they call it, spinning up and down) before they fail.

I have not noticed any crashing on my Linux laptop (set it to spin down for a few days).

And I learned it as P = VI. I'm in Canada. We use Emf, electromotive force (a misnomer, since it's not a force), too, for voltage sources (at no load, so no voltage drop due to internal resistance). For voltage drops across other circuit elements, we use V.

On the page, it says, for idle, 400mA and 0.85 Watts (5V). It matches for all other 3 (active, standby, sleep). Perhaps the current is maximum current? (Idle can include spinning up)

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Originally Posted by cyberfish

And I learned it as P = VI. I'm in Canada. We use Emf, electromotive force (a misnomer, since it's not a force), too, for voltage sources (at no load, so no voltage drop due to internal resistance). For voltage drops across other circuit elements, we use V.

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In my high school electronics class we used V when listing the number of volts & A when listing the number of amps, but E & I in formulas for some reason. This was in the early 90's, so maybe the textbooks changed?

We use V and A for units, V and I for constant voltages and currents, v and i (lowercase) for time-varying voltages and currents (first year university physics).

Maybe they use different things on the east coast (French influence?)

Not to mention it decreases the life of the drive, especially when the heads park.

The 120GB WD scorpio in my laptop parks the heads / spins down about every 10 seconds. The clicking noise is rather annoying. And it reduces the life of the drive significantly, I know it's supposed to increase the life if I dropped it, but I don't :-). So off it went.

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Originally Posted by Elysia

U stands for voltage. The standard letter (except for USA who uses V).
I suspect you are talking about the voltage you get from a battery whose term I cannot name in english. It is not different from U except the the voltage from a battery will drop as the load increases.

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U, in any equation I've ever seen, means potential energy (units == joule). Something which voltage decidedly is not.

EDIT: The P=I*V equation is only true instantaneously. For time-varying potentials or currents, the relationship must be treated as a differential one, and integrated over time.

U is the standard symbol for voltage. I don't remember if it's IEC (or whatever it's called) or simply European. But USA lists is as V, for some stupid reason.
And energy? If I remember correctly from the physics, it's unit (?) is W.
Although I haven't heard about current, we do use small u for a voltage that is not constant, such as a voltage you could measure at a certain point in time from an AC source, say.
Still, when doing calculations, it is usually converted to a constant voltage first (U).

And we must remember to separate the formulas and units (or whatever it's called in english).
We measure current in ampere, A for short, but it's written as I on formulas.
Likewise, we measure voltage in volts, V for short, but it's written as U on formulas (in Europe, at least; though not US).
These Emf formulas are mostly physics. In electronics, I haven't seen them used at all. Slightly similar formulas in magnetic fields, but not electronics... it's all about voltage (U/V), current (I) and wattage (P).

Well, SI uses V. Wikipedia page has no mention of "U", either.

U usually represents potential energy (unit J), and voltage the potential energy per unit charge (V = J/C), so you might have them confused.

Watts is a unit of power (rate of energy transfer, J/s).

Energy is measured in joules.

All these are SI (Système International) units. AFAIK, they are used by everyone EXCEPT pretty much the US (they still use imperial units - pounds, slugs, miles, yards...).
http://en.wikipedia.org/wiki/SI

You are right that most quantities have different abbreviations than their standard units, but voltage is an exception. Maybe at whereever you live, they changed it to U to disambiguate it? AFAIK, that's not a standard practice, though. Understandable, however, just like how electrical engineers use j for the imaginary unit (instead of i) since i is usually used for current in that context.

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EDIT: The P=I*V equation is only true instantaneously. For time-varying potentials or currents, the relationship must be treated as a differential one, and integrated over time.

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It happens to work for alternating currents, too, if you take the RMS of the voltage.

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Originally Posted by cyberfish

Well, SI uses V. Wikipedia page has no mention of "U", either.

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This is confusing, because I found this (in local language):
Appendix:SI-enheter - Wiktionary
Clearly, it says the symbol is U, and the unit is V.
But if you look at any USA page, it says the symbol is V.

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U usually represents potential energy (unit J), and voltage the potential energy per unit charge (V = J/C), so you might have them confused.

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I know this: here voltage's symbol is U. And USA's symbol is V.
This is how we are taught.

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Watts is a unit of power (rate of energy transfer, J/s).

Energy is measured in joules.

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I remember this part from the physics :D

The way we learned it, both the symbol AND the unit are V.

I think Elysia has got this one right. Obviously you'd have to sit in on a few physics classes in a few foreign countries to be sure, but...

First, I learned it as P=I*V and V=I*R. Not sure why you would want to use another symbol for Volts, but whatever. (What does the U stand for, Elysia?) What Elysia seems to be talking about is not the SI unit for Volt, which everybody uses V for, but rather the symbol representing it in the equation. We usually represent mass with a m, for example, but the unit is kg. F and N for force (Newtons) is the same idea.

Go look at the Wikipedia pages for Joule's Laws, in several languages.
The Italian, Spanish, Chinese pages seem to use V, whereas the Polish, French, German and Portugese pages use U. (The Ukranian page seems to use altogether different letters, but it might just be me having trouble reading it...) There also seems to be some use of the letter Q for power as well.

Yes, we agree to disagree :).

SI only standardizes units, so people can still use whatever symbols they want in equations.

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Originally Posted by Cactus_Hugger

(What does the U stand for, Elysia?)

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U is U, the symbol for voltage.
Google Translate

I learned it as V = IR when I took a class to become an electronic technician for the electrical systems in CAT mining and construction equipment. But as has been said this is an instantaneous formula and cannot readily be applied to all situations. In situations where conditions are consistent (such as voltage, resistance, and amperage) then it is a good representation of what is going on in the circuit or at least what should be going on in the circuit.

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Originally Posted by cyberfish

We use V and A for units, V and I for constant voltages and currents, v and i (lowercase) for time-varying voltages and currents (first year university physics).

Maybe they use different things on the east coast (French influence?)

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Maybe the difference is between the Physics textbooks and the Electronics textbooks then? Now that I think about it, I think I do remember P = I*V in my physics class; but the mnemonic that my electronics teacher used was "The Eagle flies above the Indian leaning against the Rock" i.e. E = I*R or I = E/R ...

Hmm I have never heard of that, but I have never taken any electronics course, either. My first circuit analysis course is in 3 months :D.

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Originally Posted by cpjust

Maybe the difference is between the Physics textbooks and the Electronics textbooks then? Now that I think about it, I think I do remember P = I*V in my physics class; but the mnemonic that my electronics teacher used was "The Eagle flies above the Indian leaning against the Rock" i.e. E = I*R or I = E/R ...

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In electrical engineering, you have to distinguish between voltage and electromotive "force" although they are both measured in volts.

Imagine a closed loop of wire with an increasing magnetic field through the center. This will cause a current to flow in the loop. But you can't talk about the voltage change around the loop, since by definition, this is zero (one point cannot have two voltages). And yet, current is flowing. So we have this weird term "electromotive force" to talk about the voltage that seems to be present, but isn't actually there.

So I think that's why they use E instead of V.