Hardware Reference
In-Depth Information
As you can see from this table, you must place an HDD that has been stored in a colder-
than-normal environment into its normal operating environment for a specified amount of
time to allow it to acclimate before you power it on.
Spindle Motors
The motor that spins the platters is called the
spindle motor
because it is connected to the
spindle around which the platters revolve. Spindle motors in HDDs are always connected
directly; no belts or gears are involved. The motor must be free of noise and vibration;
otherwise, it can transmit a rumble to the platters, which can disrupt reading and writing
operations.
The spindle motor also must be precisely controlled for speed. The platters in HDDs re-
volveatspeedsrangingfrom3,600rpmto15,000rpm(60-250revolutionspersecond)or
more, and the motor has a control circuit with a feedback loop to monitor and control this
speed precisely. Because the speed control must be automatic, hard drives do not have a
motor-speed adjustment. Some diagnostics programs claim tomeasure harddrive rotation
speed, but all these programs do is estimate the rotational speed by the timing at which
sectors pass under the heads.
There is actually no way for a program to measure the HDD's rotational speed; this meas-
urement can be made only with sophisticated test equipment. Don't be alarmed if some
diagnosticsprogramtellsyouthatyourdriveisspinningatanincorrectspeed;mostlikely,
theprogramiswrong,notthedrive.Platterrotationandtiminginformationisnotprovided
throughtheharddiskcontrollerinterface.Inthepast,softwarecouldgiveapproximatero-
tational speed estimates by performing multiple sector read requests and timing them, but
this was valid only when all drives had the same number of sectors per track and spun at
the same speed. Zoned-bit recording—combined with the many various rotational speeds
used by modern drives, not to mention built-in buffers and caches—means that these cal-
culation estimates can't be performed accurately by software.
On most drives, the spindle motor is on the bottom of the drive, just below the sealed
HDA. Many drives today, however, have the spindle motor built directly into the platter
