The DB25-pin Apple interface is commonly found on the rear of most Power Macintosh, and on virtually all earlier Macs, with the exception of the newest Apple G3's, aka the Blue and White "Yosemite", the Graphite "Yikes", and the recent Graphite G4 "Sawtooth" which lack all SCSI. The DB25 Apple connector is also found on the rear of the adapter included with the Miles Bluenote, and occasionally on the rear of some scanners.

The 50-pin Centronics interface is commonly found on external narrow hard drives, on scanners, and other external SCSI devices. The DB25 to 50-pin Centronics cable is the most common cable of all, and is generally used to attach the first external SCSI device to the rear of the Mac.

Scenarios requiring a DB25 to DB25 cable are relatively rare, but if you have an external Zip drive, and are attaching it directly to the rear of your vintage Mac, a DB25 to DB25 is appropriate.

Scenarios requiring a DB25 to 50-pin MicroD cable are also somewhat uncommon. Such a cable is required when attaching an external Plextor UltraPlex CD-R to a Macintosh, for example, or in the event you have purchased an external Castlewood Orb or Iomega Jaz with 50-pin MicroD connectors on their backplanes. Some external SCSI devices use the 50-pin MicroD interface when a smaller connector is required, as do some narrow SCSI boards like the Miles Bluenote. Flipping the DB25 to 50-pin MicroD cable around, for example, enables you to directly connect from the rear of the Miles Bluenote to an external Zip, without using the DB25-50-pin MicroD adapter included with the Bluenote.

All DB25 and 50-pin Centronics, and 50-pin MicroD connectors are 8-bit connectors, and appropriate for use on narrow SCSI buses, whether the bus specification is SCSI, SCSI-2 Fast, or SCSI-3 Ultra narrow.

The 68-pin MicroD interface is commonly found on the rear of wide SCSI boards like the Initio Miles and Miles2, the old HammerStorage JackHammer, and the Adaptec series of Ultra wide boards. Exceptions would include most dual-channel cards, which will use the smaller 68-pin .8mm Champ connector.

The 68-pin MicroD interface is also commonly found on the backplanes of external wide drives and arrays, and sometimes on the rear of some high-end external tape drives. Generally, 68-pin MicroD cables are used to connect an external wide array or wide device directly to a wide SCSI board. For SCSI-2, use standard Diagnostic Gold cables. For SCSI-3 single-ended Ultra wide, use Teflon. For SCSI-3 Differential (aka High-Voltage Differential, or Passive Differential), use Teflon. For SCSI-3 LVD/Ultra2, use LVD-rated cables. For SCSI-3 Ultra160, or Ultra3, use LVD-rated cables.

The 68-pin MicroD interface is, by definition, a 16-bit wide interface, whether the bus specification is SCSI-2 Fast & Wide, SCSI-3 single-ended Ultra wide, SCSI-3 Differential, SCSI-3 LVD/Ultra2, SCSI-3 Ultra160, or SCSI-3 Ultra320.

The 68-pin .8mm Champ connector is used in scenarios where a wide 16-bit interface is required but space is at a premium. Dual-channel SCSI boards like the ATTO Ultra3 Dual-Channel use .8mm Champ connectors, for example, as do dual-channel JackHammer and Adaptec boards. These connectors are very small--so small, in fact, that two of them can comfortably fit on the backplane of dual-channel PCI SCSI boards.

Some care in selecting cables using the 68-pin Champ connector is mandated. If you are running from the rear of a dual-channel SCSI board to an external wide device or array, for example, you will probably need a cable with .8mm Champ to 68-pin MicroD connectors. It is relatively rare that external enclosures will use .8mm Champ connectors. We do carry them, however, in the event your enclosure has them.

We can envision very few scenarios where a cable with .8mm Champ and 50-pin MicroD connectors will be appropriate, but we carry them in case you come up with one. Please be cognizant that choking a 68-pin bus down to a 50-pin connector means that you are converting a wide bus to a narrow bus. Yes, these cables properly terminate the upper-bytes.

When using a cable with an .8mm Champ connector at one end, and a 50-pin Centronics connector at the other end, you are again choking a wide bus down to a narrow bus. The upper-bytes are terminated by such cables, assuming they are built by Granite Digital, as are all cables sold by MacGurus. If you are using one channel on a dual-channel SCSI board to handle a wide external array, and the other to handle narrow SCSI devices, a 68-pin .8mm Champ to 50-pin Centronics cable may be appropriate.

The 68-pin .8mm Champ interface is a 16-bit wide interface, whether the bus specification is SCSI-2 Fast & Wide, SCSI-3 single-ended Ultra wide, SCSI-3 Differential, SCSI-3 LVD/Ultra2, SCSI-3 Ultra160, or Ultra320.

The 50-pin MicroD interface is used when a narrow connector is required but space is constrained, like on external Jaz mechanisms from Iomega, on the rear of the external Plextor PlexWriter, the rear of the external Castlewood Orb, or the backplane of the Miles Bluenote.

A cable with 50-pin MicroD and DB25-pin Apple connectors is appropriate when connecting an external device like the Iomega Jaz, Castlewood Orb, or Plextor PlexWriter to the DB25 connector on the rear of most Power Macs. A cable with 50-pin MicroD and 50-pin Centronics connectors is useful when adding a Jaz, Orb or PlexWriter to the middle of an external narrow bus.

The 50-pin MicroD interface is an 8-bit narrow interface, and is usually found on SCSI, SCSI-2 narrow, and SCSI-3 single-ended Ultra narrow buses.

The 50-pin Centronics interface used to be the most common connector of all, commonly used on narrow external drives and scanners. Very few narrow drives are made today where Ultra320 LVD now rules the roost, but the cables are all still available should you have need.

A 50-pin Centronics to DB25 Apple SCSI cable can be useful in cases where you need to connect an external drive to an external Zip, for example, while a 50-pin to 50-pin Centronics cable is typically used to attach external drives in series, or integrate a scanner into the middle of a narrow bus. A 50-pin Centronics to 50-pin MicroD cable can be useful when attaching a standard narrow SCSI device to an external Plextor PlexWriter, or to an external Jaz, or to the backplane of the Miles Bluenote.

The 50-pin Centronics interface is an 8-bit narrow interface, and is usually found on SCSI, SCSI-2 narrow, and SCSI-3 Ultra narrow buses.