The #HP9122 and #HP9134 units also are amazing. The #HP9122 is a double disk drive unit, sporting two high density drives. The #HP9134 is a MFM disk drive with a 14MB hard disk. To use mine reliably, I had to configure it as a 10 MB drive, maybe the unit was changed in the past, I haven't investigated it. I recorded it and the #sound that you can hear in this Youtube video of mine is quite characteristic given the size of the disk.

https://www.youtube.com/watch?v=xFiDVdwrSyE

#retrocomputing

Booting an HP9816 with a HP9134XV MFM hard drive

YouTube
Here is another picture of the whole set #HP9816, #HP7475A, hidden an #HP9122 and an #HP9134, the Bruël & Kjær 2034 and the #HP4277A LCZ meter.