Can prematurely powering down a computer cause bad sectors in a hard drive?

Solution 1:

Q1: Can forcibly powering off a PC without using the built-in shutdown/reboot functions, cause a HDD to accumulate bad sectors? Whether it be the result of BSODs, lockups, crashes, etc.

No. It can result in data corruption because the applications and OS did not have enough time to write pending information in memory to the disk. But it cannot result in bad sectors - all HDDs have built-in "retract circuits" that autopark the heads safely when powered off. See "Can sudden shutdown of pc can make BAD sector in HDD?"

Q2: If so, are these bad sectors repairable? I know an OS typically relocate bad sectors to other areas of the drive, but once a drive accumulates too many it just dies.

Firstly, the OS does not relocate bad sectors. The drive's firmware relocates bad sectors transparently to the OS if it finds that it's unable to reliably write to a location. Secondly, there is no "repairing" of bad sectors whose error rates are higher than what the drive's error correction mechanisms can handle. Truly bad sectors can only be relocated to a spare area of the drive (as you stated).

Reference: Error detection and correction

In any case, you should not forcibly power off a computer if you value your data. It can result in OS crashes, application crashes and loss of data.

To add to the information on autoparking HDD heads, here are a few patents (several years to decades old) related to retract circuits on HDDs (see other patents referred to within these as well):

• Hitachi Global Storage Technologies - Actuator retract circuit for dual speed hard disk drive - refers the following patents specifically related to head parking:
  • Hitachi Global Storage Technologies - multistage retract circuit for parking head carriers on power down
  • Apparatus and method for control head unloading on power down in a disk drive
  • IBM - Actuator retract/unload system for low power disk drives (using capacitors instead of the insufficient back EMF from spindle motor)
  • IBM - Disk drive with rectifier circuit for parking the head carriers on power down
• Seagate Technology - Method and means for parking read/write heads in a disc drive using the back-EMF of the spindle motor to operate a stepper motor