Hardware Reference
In-Depth Information
sensitive analog information does not have to travel along crude ribbon cables that are
likely to pick up noise and insert propagation delays into the signals. The integrated con-
figuration enables increases in the clock rate of the encoder and the storage density of the
drive.
Integrating the controller and drive also frees the controller and drive engineers from hav-
ing to adhere to the strict guidelines imposed by the earlier interface standards. Engineers
can design what essentially are custom drive and controller implementations because no
other controller will ever have to be connected to the drive. The resulting drive and con-
troller combinations can offer higher performance than earlier standalone controller and
drive setups. IDE drives sometimes are called drives with embedded controllers.
The earliest IDEdrives were called
hardcards
andwere nothingmore than harddisksand
controllers bolted directly together and plugged into a slot as a single unit. Companies
such as the Plus Development Division of Quantum took small 3 1/2-inch drives (either
ST-506/412 or ESDI) and attached them directly to a standard controller. The drive/con-
troller assembly then was plugged into an ISA bus slot as though it were a normal disk
controller card. Unfortunately, the mounting of a heavy, vibrating hard disk in an expan-
sion slot with nothing but a single screw to hold it in place left a lot to be desired—not to
mention the physical interference with adjacent cards, because many of these units were
much thicker than a controller card alone.
Several companies got the idea to redesign the controller to replace the logic board as-
sembly on a standard hard disk and then mount it in a standard drive bay just like any
otherdrive.Because thebuilt-incontroller inthesedrivesstillneededtoplugdirectly into
theexpansionbusjustlikeanyothercontroller,acablewasrunbetweenthedriveandone
of the slots. This was the origin of IDE.
Origins of ATA
Control Data Corporation (CDC; its disk drive division was later called Imprimis),
Western Digital, and Compaq actually created what could be called the first ATA IDE in-
terface drive and were the first to establish the 40-pin ATA connector pinout. The first
ATA IDE drive was a 5 1/4-inch half-height CDC Wren II 40MB drive with an integrated
WDcontrollerandwasinitiallyusedinthefirstCompaq386systemsin1986.Iremember
seeing this drive for the first time in 1986 at the fall COMDEX show. Besides the (at the
time) unique 40-pin ribbon cable, I remember being surprised by the green activity LED
on the front bezel. (Most drives up until then used red LEDs.)
Compaq was the first to incorporate a special bus adapter in its system to adapt the 98-pin
AT-bus (also known as ISA) edge connector on the motherboard to a smaller 40-pin,
header-styleconnectorintowhichthedrivewouldplug.The40-pinconnectorwasallthat
