1. 40 ground wires were added as spacers between the existing 40 wires. This both reduced cross-talk between wires and reduced the device to ground resistance.
2. The original connector configuration was poorly defined. It was not unheard of for the cables to be deliberately installed "backwards" with the connector intended for the most distant disk drive connected to the motherboard in order to accomodate a disk drive mounted near the motherboard. That often works, but it is incompatible with cable select. The 80 conductor cable has defined and color coded motherboard (blue), slave (gray) and master (black) connectors.
3. The cable select master connector was moved to the end of the cable to eliminate the 15cm unterminated pigtail present when only one device is attached to a 40 conductor cable where the master connector is in the middle.
4. The cable associated with data pins 34 in the connector was opened up between the motherboard and the drive connectors. Pin 34 is tied to ground in the motherboard connector to flag the cable as 80 conductor. The wire between the drives is left intact and is used as it always was for signaling during drive initiation. Conceptually when a 40 conductor cable with pin 34 wired through to the motherboard is used, it could conceivably be detected as an 80 conductor cable if the 40 or 80 conductor configuration is sensed while the drives are using the wire for communication.
Conceptually, either 40 or 80 conductor cables will work with older drives or with newer drives not run at very high data rates. 80 conductor cables are purportedly required for data transfers faster than 33MByte/s although it is possible that some PCs will manage without them. As a practical matter, the fact that software can determine what kind of cable is in use and can alter configurations based on that information introduces one more variable into disk setup/usage. When everything works, 80 conductor cables allow faster data transfers. When things don't work, 80 conductor cables introduce one more possible source of problems/misunderstandings.
Return To Index Copyright 1994-2008 by Donald Kenney.