Instruction manual

Page 3-4 Chapter Three
Eagle 450 Installation and Technical Manual, Rev. 00
The two cabling specifications which affect the total number of devices are:
•
The total length of the cable cannot exceed three meters (approximately 10 feet).
•
Each device must be at least one foot (approximately) from any other device.
The standard internal Wide SCSI cable for the Eagle 450 ensures adequate space between internal
devices. It allows up to five internal SCSI devices, plus the external connector. While this connector is
normally used for an active terminator, you can attach an external cable to another SCSI device. To
remain within the specification, the maximum length of the external cable is three feet. In practice, this
normally means only one external device is possible. If you need a longer external cable, use a repeater,
as described below.
To summarize, unless you use a repeater, the Eagle 450’s Wide SCSI bus supports up to five internal
devices and one external device.
If you are attaching an external device, especially if it is a narrow device, be sure to read the section on
Wide Bus Termination, below.
The Wide SCSI Repeater
As mentioned above, the total allowable bus length for the Wide SCSI bus is 10 feet. This can be very
limiting, especially in configurations which require more than one external device. The AM-441 Wide
SCSI Bus Repeater attaches to the end of the Eagle 450’s internal SCSI cable. In effect, it starts a new
physical bus: from the repeater, you can have up to ten additional feet of bus cable.
Allowing for the internal cable from the repeater to the external SCSI port, the AM-441 lets you have up
to eight feet of external Wide SCSI cabling, with as many devices as you can physically attach, obeying
the specification of at least one foot between each two devices.
The AM-441 occupies an internal 5.25” drive bay. Since there are six available bays (three of them
5.25”) and only five available connectors on the internal SCSI cable, this does not reduce the number of
internal SCSI devices you can use (the AM-441 attaches to the connector which is normally used for the
external port, so it does not take up an internal drive connector).
Narrow Devices on the Wide Bus
You can attach any narrow SCSI device to the Wide bus by using a 50-pin to 68-pin adapter, PDB-
00440-91, between the device and the cable connector. However, if you use both a narrow and a Wide
disk drive, the narrow drive’s lower transfer rate slows down the entire bus, causing the Wide drive to
lose its performance advantage. For best results, we recommend using only Wide disk drives on the
Wide bus.
On the internal cable, the order of Wide and narrow devices does not matter. If you use both Wide and
narrow external devices, the narrow device(s) must be the last device(s) on the external cable. See the
next section on how to properly terminate the bus if you have narrow external devices.