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Measuring hard drive RPM

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Franc Zabkar

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Sep 24, 2010, 10:51:26 PM9/24/10

I am aware that hard drives report their RPM via word 217 of their
512-byte Identify Device data block, but is there any utility that can
actually measure it? Nowadays Western Digital obfuscates the issue
with its Intellipower marketing speak.

The best method I have been able to find is to examine the spread of
data points in HD Tune's read or write benchmark graphs. AISI, the
total access time is the time required to seek to the target track,
plus the time required for the target sector to appear under the head.
The rotational latency can vary from 0 msec up to the time required
for one complete revolution. Hence the width of the access time graph
must correspond to the latency of one rotation. For example, a 7200
RPM drive would have an 8 msec wide access time graph.

Here are more HD Tune results which show how RPM affects access time:

WD15EARS-00Z5B1 - 5400 RPM ?
http://sylphys.ddo.jp/upld2nd/pc3/src/1267687303631.png

WD15EADS-00P8B0 - 5400 RPM ?
http://ettcweb0.aa0.netvolante.jp/log/20090830004.png

ST32000542AS Barracuda LP - 5900 RPM:
http://users.telenet.be/Mastakilla/HDs/6XW19HYS_write2.JPG

WD2001FASS-00U0B0 - 7200 RPM:
http://dl6.getuploader.com/g/6%7Cnews23/18/HDTune_Benchmark_WDC_WD2001FASS-00U0B0%5B64kB%5D.png

WD5001AALS-00L3B - 7200 RPM:
http://bbsimg01.kakaku.com/images/bbs/000/236/236059_m.jpg

WD1500HLFS-01G6U0 - 10K RPM:
http://dl7.getuploader.com/g/6%7Cnews23/20/HDTune_Benchmark_WDC_WD1500HLFS-01G6U0.png

ST3600057SS - 15K RPM:
http://images.kbench.com:8080/kbench/article/2009_09/k73831p1n6.jpg

- Franc Zabkar
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