HP 220mx User Manual page 97

Operating This Jukebox on a SCSI Bus
The SCSI Bus and This Jukebox
Because a narrow device only has a 50-pin connector, it will not transmit the eight
extra bits of data needed for the wide device on the end of the bus. Using only 50
lines also prevents the narrow device from passing along the IDs of devices at 8 or
above.
The lower eight data lines transfer commands and messages, allowing all devices,
regardless of size, to co-exist on the bus. However, data transfers and device
addressing occur on the higher bits. Since a narrow device can't "see" the upper 8
data bits, that translates to it not being able to "see" wide devices with a SCSI ID
above 8. Remember the host adapter is a device, so if you're mixing wide and
narrow devices on the bus, your host adapter must be at an ID that all devices can
address.
If mixing narrow and wide devices is unavoidable, use the configuration described
below:
Appendix B B-9