What is an 80 conductor cable?
The 80 conductor cable is a new type of cable for attaching ATA (IDE) disk drives to systems or controller cards. It has 80 wires in the ribbon cable. Older ATA cables always had 40 conductors (drive connectors have 39 pins, one is removed as a key).
How Does It Work?
Every other line of the 80 conductor cables is tied to ground inside the connector. This results in a much better signal quality as the crosstalk (signals from adjacent lines coupling into each other) and ground bounce are greatly reduced. The cable is backward compatible with all old ATA drives, other than 2.5" drives. The connectors still have 40 pin sockets. Ultra ATA/66/100 drives still have 40 pin connectors.
UltraATA/66/100
UltraATA/66/100 is the new data transfer rates. The 80 conductor cable is required to run at 66/100 Megabytes/s. The cable was designed for automatic detection. When using UltraATA/66/100 a system must check to see if an 80 conductor cable is installed. If one of the lines (PDIAG) is grounded then is an 80 conductor cable. If the line is not grounded then it is a 40 conductor cable. Systems should automatically switch to UltraATA/33 mode if they sense a 40 conductor cable.
Cable Select
All 80 conductor cables support the Cable Select feature. If you set the drive address (Master/Slave) jumper to Cable Select then the drive uses the cable to determine if it is Drive 0 or Drive 1. Drive 0 is always the drive on the other end of the cable (black connector) from the system. Drive 1 is the drive near the middle (gray connector) of the cable.
Odd/Even
Due to the fact that the connector manufacturing companies rarely agree on anything there are two types of 80 conductor connectors, odd and even. Some manufacturers run the ground lines down the even wires and some run them down the odd wires in the 80 conductor cable. This is a problem only for cable assemblers. If you mix the two types of connectors on the same cable it shorts all the lines together. Once the cable is assembled correctly there is no problem.
This is not a problem for drives or systems as they still have 40 pin connectors.
To Sum Up:
80 Conductor Ribbon Cable
Required for UltraATA/66/100 Speed
Improved Signal Quality
Ground on all even lines or all odd lines in the cable
40 Pin Sockets on Cable (Just like before)
40 Pin Connectors on Drive (Just like before)
Backward compatible with all 3.5" drives
Supports Automatic Cable Type Detection
Supports Cable Select
Source: dslreports.com
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