Note: Nowadays, the connectors on the scsi hard drives are either High Density 68-pin or SCA 80-pin. Hard drives with SCA 80-pin connectors are also known as Hot-Swap or Hot-Plug drives and do not connect directly to the scsi cable. (If you have an 80pin drive and want to connect it, the less expensive solution is to use the 80pin-to-68pin converter). By looking at the last two letter on the hard drive model you can usually tell if it is High Density 68-pin or SCA 80-pin. (see chart below) For example Seagate ST3146807LW is a HD 68pin drive.
Note: Most commonly encountered on scsi cards are the VHDCI 68-pin, High Density 68-pin, and High Density 50pin.