There are four main types of external SCSI connectors - the plugs and sockets used to connect SCSI devices. Some have 50
pins, and are used for narrow SCSI, while others have 68 pins and are used for wide SCSI. Mixing wide and narrow SCSI
devices on the same chain is possible but may cause problems, especially if the extra wires from the wide SCSI devices are
not terminated.

D-Shell, D-Sub, DB or 3-Way
This is the oldest type of SCSI connector. It has 50 pins arranged in 3 rows, surrounded by a D-shaped metal shell for shielding. It is larger and more cumbersome than the other types of SCSI connector, and is only common on old machines.
Instead of the usual pins, these connectors have two rows of thin metal contacts attached to both sides of a piece of plastic in the centre of the connector. These are also quite old and only used for narrow SCSI.
High-Density, HD or Micro-SCSI
These use pins like the D-Shell connectors, but the space between the pins is much smaller, which makes the connectors easier to use. They come in both a narrow version with 50 pins and a wide version with 68 pins.
Very High Density Cable Interconnect, VHDCI or Micro-Centronics
These are the newest type of connector, and only come in a wide version with 68 contacts. They look exactly like a Centronics connector except that the contacts are much smaller.

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