REDISKME llc - Data Recovery in Santa Cruz, CA - What is a disk crash?

Hardware disk crashes

A computer hard disk is an electro-mechanical device that reads and writes data magnetically to a spinning disk. The disk is able to hold the data through being covered in a very thin layer of what amounts to magnetically sensitive paint. The drive might have multiple disks or platters all being read from and written to. The disk(s) spin at very high speed with the slower models spinning at 5000 rounds per minute (rpm) and the fastest at 12,000 rpm or higher. The device that reads and writes is called a read/write head. The read/write head is attached to a control arm that moves it back and forth across the disk. The control arm might have multiple read/write heads servicing the top and bottom of the disk(s).

When the read/write head writes data it also reads it back to determine if the data was written correctly. The data is compared to a memory buffer in the drive electronics. When the data has been safely written the data is purged from the buffer so more data can be written. When disk determines that the data it has written cannot be read back reliably it marks that section of the disk as bad. This bad section of the disk is referred to as a bad cluster or bad sector. All hard drives have bad sectors even when they are new. The drive electronics compensate for bad sectors by keeping certain sections of the disk free for the sole purpose of rewriting bad sectors. This excess capacity is typically not cited for the purpose of determining the size of a new hard disk.

Over time the disk develops more and more bad sectors until one day the drive can no longer rewrite or remap damaged sections of the disk. This is about the time that the average computer user starts experiencing symptoms. The symptoms will vary depending on what program code or data is located on a now unreadable sector of the disk.

Any section of a disk can become unreadable for a variety of reasons. The read write head might periodically touch the spinning disk due to a power failure or a power spike. Slowly the magnetically sensitive layer on the disk just naturally degrades.

Electrical shock may cause damage to the disk. Also, the drive electronics might malfunction because the circuits crack or become contaminated with dust due to mishandling. Disks also fail due to the electronic circuits cracking through expansion and contraction as the disk heats up and cools down with normal usage.

When a disk crash is caused by hardware it is extremely critical to remove or backup your important data from the disk as soon as possible. Hard disks typically crash partially and then at some point later they fail totally. As more time goes by with a hardware based disk crash the probability of being able to recover important data from the disk is greatly diminished.