HP 9000 300 Series Service Training page 43

Mass Storage Devices (2)
Note
Mass Storage Devices (2)
Integrated
Top Slot 3.6 Only
Middle Slot Custom Assembly.
Bottom Slot 62 or 400
The middle slot is wired for possible future use of the 3.5 floppy and hard
drives. At this time, there aren't any trays that have holes for mounting the
hard drives. There is for the floppy, but it is not formally sold as an upgrade.
3·6 Theory of Operation