Hi Don,

150 is the maximum interface speed. The disk being a rotational device is
governed by physical laws constrained by the platter rotation speed and bit
density on the platters. Regardless of how fast the interface is, you can't
get the bits off the platter any faster than they pass under the read/write
heads. You may get a very short burst faster than the platter speed as data
is pulled out of the cache, but the cache is exhausted in a fraction of a
second.

To make it more complicated, the bit density varies between the inside and
outside tracks of the platters, so that the measured speed depends on where
the test was performed physically on the disk.

Most disks these days spin at 7200RPM, with lower end and most notebook
drives running at 5400 RPM. Higher end disks like the Western Digital Raptor
spin at 10000RPM, but are considerably more expensive. At the very high end
are Seagate Cheetah disks (usually SCSI or fiber only) that spin at
15000RPM. These are typically employed in servers.

HTH,
Russ Poffenberger
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-----Original Message-----
From: Personal Computer Hardware discussion List
[mailto:[log in to unmask]] On Behalf Of Don Penlington
Sent: Wednesday, December 27, 2006 10:21 AM
To: [log in to unmask]
Subject: [PCBUILD] Hard Drive Speed test


XP Pro SP2.

In Device Manager/IDE Controllers/ Secondary Channel,  when I run the speed 
test for my Hard Drive (Serial ATA DMA) it says that the theoretical speed 
is 150. The Burst speed on test is 113 and sustained speed is 58.

These test figures seem to me to be way short of the theoretical speed.  Is 
the theoretical speed that for an "ideal" HD, or is it the theoretical 
speed for my actual HD?

Should I be worried, or are these results normal?

I don't seem to have any problems---just curious.

Don Penlington

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