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Table Of Contents  CertiGuide to A+ (Core Hardware)
 9  Chapter 0100:  Hard Drives
      9  VII  IDE

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Primary (Master) / Secondary (Slave) / Cable Select (CS)

No matter how you look at it, IDE can only support 2 devices, period.

2 Drives Per Controller

IDE
/EIDE/ATAPI, Etc., can only support two drives” on each controller

Since IDE was so cool, manufacturers added a second IDE controller to the ATX system board, giving the possibility of four drives. When this happened, the first IDE channel was known as the Primary IDE channel. The newer one became known as the Secondary IDE channel.


Figure 51: 40-pin IDE HDD with jumper set to stand-alone.

 


Since all the drives were intelligent, or had integrated control, it would create havoc to have BOTH drives attempting to control the show. The terminology that resulted was the drive that controlled the show became known as the Master Drive. The other drive had its control circuits turned off, and was called the Slave Drive.

I hope this poor choice of terms would slowly disappear for the new choices IDE Channel 0 (or) 1, while the second IDE channel could be known as Channel 1 (or) 2.

The drive known as master could be known as the Primary drive (replacing the designation used for the channel) and the drive formerly known as slave could be replaced with the term secondary drive, replacing the name for the second IDE channel.

Regardless of the terms, jumpers have to be used to turn on the controller, or turn it off. A way around this is to use the cable to select which drive will control the show. Enter Cable Select (CS) cable.

[spacer]Cable Select Becomes Jumperless

80
conductor IDE cables (and IDE CS cables) have Pin 28 connected to the drive and the system board or host adapter. This turns on the controller. There is no attachment for Pin 28 for the second drive, so its controller is not used.


Except for some 'value priced' PCs, cable select never caught on, and the regular 40 conductor IDE did not support CS, requiring a CS cable. The drive with the controller turned on in a CS configuration requires that drive be in the middle of the IDE cable (perhaps why CS never caught on).

Finally, as mentioned above, CS is automatically supported in the 80 wire IDE cable, and reverses (to the way it should be) to where the controlling drive is at the end of the cable. Be careful when working with CS systems.


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