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Old 05-23-2004, 10:28 AM   #1
jwstric2
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notebook hard drive power rating


This is more of a hardware than linux-hardware issue. Does anyone know how manufacturers rate the power for reads and writes on hard drives? They rate them as say an average write being 450mA. What is average? Is this a rating per block basis?

Thanks in advance
 
Old 05-23-2004, 09:08 PM   #2
ilikejam
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Hi.

450mA is how much current the drive draws when it's writing - it's not a time / per-block thing. It will continue to draw this much current until it's finished writing and returns to its lower current idle state, so if you want to know how much capacity it takes out of your battery (I assume this is what you really want to know), then you have to multiply the 450 by the amount of time the drive spends writing (in hours usually), then multiply that by the supply voltage of the drive to get a figure in mWh (milliwatt-hours). Battery capacities are measured in mAh or milliamp-hours, so to get the total number of watt-hours your battery can hold, multiply the figure in mAh by the voltage of the battery. You can then see how much of your battery's capacity is used for the amount of time the drive was writing for.

If it is actually the *power* you want to know then it's 0.450 (in this case) x supply voltage (I think it's 5V for laptop drives, but I could be wrong), so the power used when writing would be 2.25W.

Dave
 
  


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