Hardware Reference
In-Depth Information
failed drive by replacing the logic board rather than the entire drive. Replacing the logic
board,moreover,enablesyoutoregainaccesstothedataonthedrive—somethingthatre-
placing the entire drive does not provide. Unfortunately, none of the drive manufacturers
sell logic boards separately. The only way to obtain a replacement logic board for a giv-
en drive is to purchase a functioning identical drive and then cannibalize it for parts. Of
course,itdoesn'tmakesensetopurchaseanentirenewdrivejusttorepairanexistingone
except in cases in which data recovery from the old drive is necessary. Cannibalizing new
drivestorepairolddrivesisacommonpracticeamongcompaniesthatofferdatarecovery
services. They stock a large number of popular drives they can use for parts to allow data
recovery from defective customer drives they receive.
Most of the time, the boards are fairly easy to change with nothing more than a screw-
driver. Merely removing and reinstalling a few screws as well as unplugging and recon-
necting a cable or two are all that is required to remove and replace a typical logic board.
Cables and Connectors
HDDs typically have several connectors for interfacing to the computer, receiving power,
andsometimesgroundingtothesystemchassis.Mostdriveshaveatleastthesethreetypes
of connectors:
• Interface connector(s)
• Power connector
• Optional ground connector (tab)
Of these, the interface connectors are the most important because they carry the data and
command signals between the system and the drive. In most cases, the drive interface
cables can be connected in a daisy-chain or bus-type configuration. Most interfaces sup-
port at least two devices. Older interfaces, such as ST-506/412 or ESDI (Enhanced Small
DeviceInterface),usedseparatecablesfordataandcontrolsignals,buttoday'sSCSI,ATA
(AT Attachment), and SATA drives have a single data connector on each drive.
See
“
PATA I/O Connector
,”
p.
377
(
Chapter 7
, “
The ATA/IDE Interface
”
).
The power is supplied via the larger 4-pin peripheral power connector found on all PC
power supplies. Most HDDs use both 5- and 12-volt power, although some of the smaller
drives designed forportable applications use only 5-volt power.Inmost cases, the 12-volt
power runs the spindle motor and head actuator, and the 5-volt power runs the circuitry.
Make sure your power supply can supply adequate power for the HDDs installed in your
system.
The 12-volt power consumption of a drive usually varies with the physical size of the
unit. The larger the drive is, the faster it spins. In addition, the more platters there are to
