to attach external SCSI devices to the 040 NeXTs?
SCSI cable to NeXT Yes. This cable is the same as the one used by Sun SparcStations and DecStation 5000’s (but not DecStation 3100’s which use 68-pin micro rather than the 50pin micro connector used on NeXT 040, Suns and DecStation 5000). The implication that a Sun SparcStation cable can be used with NeXT peripherals is generally false. NeXT themselves, and DEC, and nearly everyone else who makes SCSI peripherals, puts Telco-50 (centronics) connectors on their devices. Sun in their infinite wisdom uses DD50 which are quite different. Telco-50 is an approved connector type in the SCSI spec. Probably the original point was that the 50-pin microSCSI on the NeXT and Sun and some DecStations was different from the 68-pin microSCSI on the DecStation 5000. But this does not address the other end of the cable.
