The servo system also has a finite response time to react to feedback information which informs the system that the heads are moving off track. If external influences such as shock or vibration act to misposition the data heads, then recording or readback data errors will occur. The high track densities of today's disk drives impose formidable requirements on the servo positioning system. A positioning error on the order of tens of micro inches is sufficient to cause errors. The lubricated bearings contained in the disk spindle and voice coil actuator and the read channel and servo channel electronics are all thermally sensitive components.
Cold temperature increases the viscosity of the lubricants used in the bearing systems.
This effect has been known to create functional problems. Changes in the voice coil actuator bearing lubricant viscosity may cause instability in the servo positioning loop. These conditions are created aboard aircraft when parked with the environmental control systems deactivated. These effects, while not permanent, prevent proper operation when systems are first turned on after extended cold periods. Extreme high temperature also has a negative effect on bearing life and head media reliability due to bearing lubricant outgassing.