Hardware Reference
In-Depth Information
air cushion is disturbed by a particle of dust or a shock, the head can come into contact
with the platter while it is spinning at full speed. When contact with the spinning platters
is forceful enough to do damage, the event is called a
head crash
. The result of a head
crash can be anything from a few lost bytes of data to a completely ruined drive. Most
drives have special lubricants on the platters and hardened surfaces that can withstand the
daily “takeoffs and landings” as well as more severe abuse.
Many newer drives do not use CSS design and instead use a load/unload mechanism that
does not allow the heads to contact the platters, even when the drive is powered off. First
used in the 2 1/2-inch form factor notebook or laptop drives where resistance to mechan-
ical shock is more important, load/unload mechanisms use a ramp positioned just off the
outer part of the platter surface, whereas some newer designs position the ramp near the
spindle. When the drive is powered off or in a power-saving mode, the heads ride up on
the ramp. When the drive is powered on, the platters are allowed to come up to full speed
before the heads are released down the ramp, allowing the airflow (air bearing) to prevent
head/platter contact.
Because the platter assemblies are sealed and nonremovable, the track densities on the
disk can be high. Hard drives today have up to 270,000 or more tracks per inch (TPI)
recorded on the media. Head disk assemblies (HDAs), which contain the platters, are as-
sembled and sealed in clean rooms under absolutely sanitary conditions. Because few
companies repair HDAs, repair or replacement of the parts inside a sealed HDA can be
expensive. Every hard disk ever made eventually fails. The only questions are when the
failure will occur and whether your data is backed up.
Caution
It is strongly recommended that you do not even attempt to open an HDD's HDA unless you
have the equipment and expertise to make repairs inside. Most manufacturers deliberately
maketheHDAdifficulttoopentodiscouragetheintrepiddo-it-yourselfer.OpeningtheHDA
voids the drive's warranty.
Note
Although you should never open a disk drive to attempt to repair it, disk drives can operate
without a cover. In some of my PC Hardware and Troubleshooting or Data Recovery sem-
inars, I have even removed and installed the covers while the drives were operating! Those
drives continue to store data perfectly to this day with their lids either on or off. Keep in
mind, of course, that these drives don't contain any valuable information.
If you want to see what hard disks look like on the inside without opening them up, I
suggest checking out the Red Hill Hardware Guide's “old gold” hard drive history page at
