PaulSanderson wrote:
The issue re coil actuators moving a different way is probably not relevant as a modern drive has embedded servo so the heads 'know' where they are.
Yes, but at least in theory it is possible that the head will *somehow* get "there" more "exactly".
Only seemingly OT, but until a few years ago the usage of high precision measuring instruments (such as theodolites):
http://en.wikipedia.org/wiki/Theodolite
implied (when higher precision of measurement was required) to do what in Italian is called "giri di strumento", cannot say the exact English translation, it would be equivalent to "instrument turns", you (besides doing the "normal" 180° "reverse" reading) turned the instrument 360° two times, approaching the needed angle (or targeting the actual reference) once "from the left" and "from the right" in order to correct the (possible) "collimation error", due to (very minimal) possible differences in the way you "approach" the desired position.
The same mechanical principle may apply to a pivoting heads arm.
PaulSanderson wrote:
Re the heating up issue - this is probably due to hysteresis as the drive logic causes the heads to recalibrate (by seeking to track 0 - you can usually hear this on a failing drive) after x failed reads.Not only <img src="images/smiles/icon_eek.gif" alt="Shocked" title="Shocked" /> , as I see it, if we take as "general reference" some 3 hours to image a 500 Gb hard disk (perfectly functional) we are essentially "stress testing" it for continuously reads for 3 hours.
This cannot be considered "normal" activity for a hard disk, that in the same three hours of use may sleep a bit, read some data, write some other, run idle a bit (before going to sleep), etc., I would define it "intensive" activity.
What happens with a "dumb" imaging program that will insist on the same area over and over (and still read not properly the data)?
The same "stress test" will be prolonged for several hours or days, which is not a good thing as it makes more probable that *something* may fail (of course it greatly depends on the nature of the "initial" reason for the bad area(s), but still) it makes more sense to stress the least the poor little thing and though there is not a definite correlation between (over) heating and disk failures the available data suggest that to be on a "safer" side it is better if the disk is kept within a not-to-hot and not-too-cold temperature range.
jaclaz
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