HP SureStore Optical Jukebox 160ex Service Manual page 209

Theory of Operation
Configuring This Jukebox on a SCSI Bus
would be lost if the devices were set up as depicted in the figure below.
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. The host adapter is a device,
so if mixing wide and narrow devices on the bus, the host adapter must
be at an ID that all devices can address.
If mixing narrow and wide devices is unavoidable, use the configuration
described on the next page.
Chapter 6 6-17