Fundamental of Hard Disk Drive Technology (6)

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• To achieve these demands ⇒ Use a servo-controlledDC spindle motor Same technology as is used in a voice coil actuator• Platters: Are machined with a hole the exact size of the spindleAre placed onto the spindle with separator rings (spacers)between them to maintain the correct distance and provideroom for the head armsContinuous Power vs. Peak Power at Spin-Up• 12V power profile of an IDE/ATA hard disk at startup• Require power management systems
Power Management• A set of protocols used to allow PCs to reduce theamount of power that they consume, especially whenthey lie idle.• An example of power management schemes: The HDD's spindle motor can be "spun down" after acertain amount of inactivity, and then can be "spun up"(reactivated) when the system needs it again. Controversy ⇒ How much energy is really saved?• Laptop users need power managementAll laptop HDDs support power management via BIOSsettings and/or operating system controlsSpindle Motor Bearing• A critical component of the HDD's spindle motor is theset of spindle motor bearings.• Bearing are precision components that are placedaround the shaft of the motor To support them and ensure that the spindle turnssmoothly with no wobbling or vibration• Increasing spindle motor speed requires many designchallenges to keep vibration and heat under control.• Two spindle motor bearings depending on mechanicaldesign, i.e., ball bearing and fluid-dynamic bearing.Ball Bearing (BB)• Used in HDDs for many years• Small metal balls are placed in a ring around the spindlemotor shaftMagnet• Non-Repeatable Runout (NRRO) ⇒ any runout of thebearing that does not repeat when the appropriate ring,inner ring or outer ring, is rotated one completerevolution. Cause Track Mis-Registration Impact HDD performance• BB motors produce large NRRO due to the mechanicalcontact (metal balls).• There is an upper limit at which the BB design can nolonger overcome the NRRO problem at the higher arealdensities.Ball Bearings ⇒ NRRO has settled in the 0.1 micro-inchrange
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Fundamental of Hard Disk Drive Technology (6)

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