IDE stands for Integrated Device Electronics.
An IDE interface is a way of connecting a device, typically storage, to
a computer system. The IDE interface was originally used to integrate
hard disk drives to a computer system. Over time a number of other devices
have come to use the IDE interface including CD-Rom drives, tape drives,
zip drives, etc.
The IDE interface was developed as a way of increasing the
performance and cost of mass storage on computer systems, namely the hard
disk. When hard disks were originally added to computer systems there
were two discrete componants that were required to accomplish the addition.
First was the disk drive and the second was disk controller electronics,
or controller card.
As performance increased in computer systems the mechanical
disk drive often became the target of performance improvement. It was
a well known problem of the separation of the hard disk drive and the
controller electronics. The two componants were generally made by two
different manufacturers with different standards and concepts as to how
everything should be implemented. To make matters worse it was very important
that each manufacturers products were compatible with everyone elses product.
The only way to achieve total compatibility was by hindering performance.
The disk drive manufacturers knew that if they were to "integrate"
the controller into their hard disk they would be able to tune the performance
of each with the other. This tuning would enable maximizing performance
of hard disk storage technology and changing hard disk technology forever.
An IDE channel, of which there can be up to four, can support
three distinct configurations of devices connected to that channel. The
configuration is performed on the IDE device itself, typically with jumpers.
The IDE channel is identified by the connection of a single cable to an
IDE port on a computer system. If there is more than one cable, then there
is more than one IDE port on the computer.
The first configuration is that of a single device. This
configuration is where there is only one single IDE device connected to
the IDE cable and port. When configured in this manner the IDE device
must be set distinctly as a single IDE device.
The second configuration is that of a master device. This
configuration is where there are two IDE devices connected to the same
IDE cable and port. When using this configuration only one of the devices
that are connected to the same cable and port may assume the role of the
master device! When configured in this manner the IDE device must be distinctly
set as a master IDE device.
The third configuration is that of a slave device. This configuration
is where there are two IDE devices connected to the same IDE cable and
port. When using this configuration one of the devices is configured as
the master device and the other is configured as the slave device. When
configured in this manner the IDE device must be distinctly set as the
As far as I am aware there is only one manufacturer who strictly
adheres to the three distinct states and has a jumper setting for each
state. That manufacturer is Western Digital, every other device manufacturer
combines the master and single configuration into one single setting.
For this reason is is very important when adding a second IDE device to
the same cable to determine if the first device has the "single"
configuration. If so then you must change that device from the simgle
configuration to the master configuration.
The single, master, and slave rules only apply when connecting
devices onto the same cable. If they are connected to different cables
(different IDE ports) it is as though they were by themself.