ReActiveMicro MicroDrive Turbo, Owner'S Manual, Page: 49 / 55

MicroDrive Turbo 42 ReActiveMicro
Many people who use systems with ATA connectors on the motherboard believe that
a hard disk controller is built into their motherboards, but in a technical sense the
controller is actually in the drive. Although the integrated ATA ports on a
motherboard often are referred to as controllers, they are more accurately called host
adapters (although you’ll rarely hear this term). A host adapter can be thought of as a
device that connects a controller to a bus.
IDE Origins
The earliest IDE drives were called Hardcards and were nothing more than hard
disks and 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 assembly then was plugged into an ISA bus slot as though it were a
normal disk controller, this concept was quite popular with Tandy based PC
Compatible Computers.
Unfortunately, the mounting of a heavy, vibrating hard disk in an expansion slot with
nothing but a single screw to hold it in place left a lot to be desired—not to mention
the possible 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
assembly on a standard hard disk and then mount it in a standard drive bay just like
any other drive. Because the built-in controller in these drives still needed to plug
directly into the expansion bus just like any other controller, a cable was run
between the drive and one of the slots.
These connection problems were solved in various ways. Compaq was the first to
incorporate a special bus adapter in its system to adapt the 98-pin AT (ISA) bus edge
connector on the motherboard to a smaller 40-pin header style connector the drive
would plug into. The 40-pin connectors were all that was necessary because it was
known that a disk controller never would need more than 40 of the ISA bus lines.
Control Data Corporation (CDC), Western Digital, and Compaq actually created what
could be called the first ATA-IDE interface drive and were the first to establish the
40-pin ATA connector pinout. The first ATA IDE drives were 5 1/4-inch half-height
CDC 40MB units with integrated WD controllers sold in the first Compaq 386 systems
in 1986, all of which made Compaq a forefront competitor to IBM in the early years
of the PC marketplace.
Eventually, the 40-pin ATA connector and drive interface design was placed before
one of the ANSI standards committees that, in conjunction with drive manufacturers,
ironed out some deficiencies, tied up some loose ends, and then published what was
known as the CAM ATA (Common Access Method AT Attachment) interface.
The CAM Committee was formed in October 1988, and the first working document of
the AT Attachment interface was introduced in March 1989.