Integrated Drive Electronics (IDE) is the name for the AT Attachment (ATA) design, and
IDE has the drive controller built into the drive itself.
Still, an IDE can connect to the motherboard bus by connectors embedded in the motherboard,
or by connecting to an expansion card in an ISA or PCI slot.
The cost of producing a motherboard with the embedded IDE connectors is less
than having an additional controller board installed in an expansion slot. Consequently,
most motherboards available today will have multiple embedded IDE connectors.
CONNECTORS Most modern motherboards have two IDE connectors (a Primary and a Secondary
IDE connector), as well as an "auto-detect" for IDE boards. An IDE connector
is a 40-pin plug. You can only attach two devices to an IDE cable. Most motherboards
have two 40 pin connectors, as does most IDE expansion cards.
So, if you have a motherboard with a built-in IDE interface, it will normally have
3 sets of connector pins. You can connect floppy drives, hard drives, CD-ROM drives,
etc. However, you may want more drives, and if you elect to go IDE, you
can purchase a "controller" card that you can place in an "expansion" slot
on the motherboard. This will allow you to connect two additional cables
for 4 more devices.
Some motherboards have the IDE connectors interfacing to a VESA Local Bus, with
the labels "VESA IDE" and "VESA ISA", and have one set of pins without a label.
We connect the hard drives to the "VESA IDE" connector, the floppy drives to the
unlabeled connector, and the CD-ROM to the "VESA ISA" connector.
An IDE connector interfaces to a maximum of two devices. The cable to connect
devices is a flat ribbon cable with 3, 40 pin, connectors. The end of the cable
with the connectors close together connects to the devices, and the long end
connects to the IDE connector on the motherboard. One side of the cable has a
RED edge. The RED edge goes to
pin 1 on the device and pin 1 on the motherboard connector.
IDE Drive Capacity
Original ATA limitations were that a maximum addressing of 528 MBytes was
the limit. This is still a problem in many older PC's with a BIOS predating
about 1991. With the newer capacity hard drive devices, a solution had to
be reached. See "EIDE" discussion and the "SCSI" discussion.
SPEED:
Pure IDE devices are somewhat slow, usually at a 8 MHz cloack, an 8 bit AT interface
connection can move data at 4 MBytes per second; in a 16 bit form, it can move up to
8 MBytes per second. Reference SCSI and EIDE discussions for higher data rates.
CD-ROM interface to an IDE interface was achieved through development of
the AT Attachment Packet Interface (ATAPI) introduced around 1993. This allowed
attachment of CD-ROM drives to an IDE connector.
An excellent discussion is included in the "Winn L. Rosch Hardware Bible" from
SAMS Publishing, and in "Upgrading and Repairing PCs", from QUE Corporation.
The term "Integrated Drive Electronics" (IDE) appeared in 1986, as Compac Corporation,
Western Digital, and Magnetic Peripherals division of Control Data Corporation
worked together to integrate a Western Digital controller chip onto a hard disk
drive. In 1988, an industry group called Common Access Method (CAM) was formed
and developed a standard that was submitted to the American National Standards
Institute in November, 1990. The standard was approved in 1991 as the AT standard.
Today we call it an "IDE" standard.
EIDE Interface